We are trying to figure out how long it will take Peter to rake 8 bags of leaves, so we'll call that Y. And we know Peter can rake 3 bags of leaves / 15 minutes = 8 bags of leaves / Y.
Next, we will multiply to find the cross-products. 3 x Y = 15 x 8 or 3Y = 120.
We want to get figure out Y, so we need to get it by itself by dividing by 3, like this: 3Y/3 = 120/3 or Y = 40 minutes.
#### 40