Easiest way is to work backwards:

Step 1: Subtract 5 apples picked at tree 4 Leaves 60 apples

step 2: Divide by 5, the increase after tree 3 Leaves 12 apples

Step 3: Each picked same amt at tree 2. Divisors of 12 are 3 & 4. Each must have picked 3 else there would be no apples from tree 1. Leaves 3 apples to go.

Each must have picked just one apple from tree one.

Step 1: Subtract 5 apples picked at tree 4 Leaves 60 apples

step 2: Divide by 5, the increase after tree 3 Leaves 12 apples

Step 3: Each picked same amt at tree 2. Divisors of 12 are 3 & 4. Each must have picked 3 else there would be no apples from tree 1. Leaves 3 apples to go.

Each must have picked just one apple from tree one.