Now we're going to solve word problems that have the word left in them. We're going to write an equation to represent the word problem and solve it. So in math, when we see the word left normally indicates that we're starting with some amount of something, we're taking a part of it away, and then we want to see what amount is left. So since we're taking something away, we're going to deal with subtraction. So we want to keep that in mind when we look at this next word problem. Jessie saved some money to go to the store. She gave $7.50 to her little sister and now has $12.80 left. How much money did Jesse start with? Write an equation and solve. Okay, let's make sure we understand what's going on in the word problem. Okay, so we see that we have Jesse who has some money. She goes to the store and she gave $7.50 to her sister. So she has some of her money given away. That's going to be subtracted from what she started with. And now she has 12.80 left. We're asked to figure out how much money Jesse started with. So how much does she have in the beginning when she went to the store? Okay, now the problem is making sense. Let's look for the information that we need to set up our equation. We want to look for the variable which is based on what we are asked to find. We're asked to find how much money Jesse started with. That's our unknown. So we're going to use a variable to represent it. Since we have money, let's use M. We'll use M to equal the money that Jesse started with. Next, let's look for our numbers and figure out what those numbers represent. Let's see $7.50. That's what she gave away to her little sister. Okay, that's important to know. And then the other number we have is $12.80. That's the money that she has left now. Okay, so there's the important things that we need. We have a variable, M, the money that she started with, $7.50 that she gave to her sister. $12.80 that she has left. But we need to know what operation is going to put all this information together. We mentioned since we're talking about how much she has left, that means that some money was taken away, which is the money that she gave her sister. So we have subtraction here. We're going to start with the money that she had in the beginning, which was M. And now we're going to subtract from the 7.50 that she gave her sister. And that will equal the amount that she has left, the $12.80. There we go. We just set up our equation. Now we just need to solve for M. So we know the amount of money that Jesse started with. So we want to isolate our variable M, which means we have to do the opposite of subtracting 750. So we have to add 750. Do that on both sides. Now we'll simplify both sides of this equation. On the left side we have m -750 and then plus 750. Those 750s will cancel each other out, it equals zero. So on the left we'll have M plus zero. And on the right we'll add the $12.80 plus the $7.50. So on the right, we'll have $20.30. All right, now we have m plus zero equals $12.30. But we don't need that zero, do we? Because m plus zero is just equal to M. So we can write this as M equals $20. Our equation is solved. We have our variable M, isolated by itself on one side, our equal sign in the middle. And our solution, our number isolated on the other side by itself. Which is the $20.30. So m was the amount of money that Jesse started with. So we just figured out what that value is. So Jesse started out with $20.30. We just learned how to set up an equation to solve this word problem.