Apple per box: 5*2= 10 (kg)

Explanation: Because each box of apples is twice as many as each box of grapes, 5 boxes of apples = 10 box of grapes, 5 boxes of apples and 5 boxes of grapes = 15 box of grapes.

So each box of grapes weighs 75/ 15=5 (kg).

Each box of apples weighs 5*2= 10 (kg).