The tape diagram is shown above the problem. If you count each box as 5, the children tape counts up to 25 as the problem says. Therefore, if we count the easel boxes, we get a total of 15.
Another way to solve this problem is the cross multiply divide method.
x/25 = 3/5
We need to find a way to make these two fractions equal. We can put an x for the unknown value, and then solve for it.
(x/25)*25 = (3/5)*25x = 75/5x = 15