There are two boxes of apples. The number of the first box is four times that of the second box How many in the second box?

There are two boxes of apples. The number of the first box is four times that of the second box How many in the second box?

Suppose the number of apples in the second box is x, then the number of apples in the first box is 4x
4x-15 = x + 15, then x = 10, then 4x = 40, that is 40 apples in the first box and 10 apples in the second box