Puzzle ZWSM 

Workings

Hint
In the first box, look at 7 & 3, and 4 & 1, to see how we can use them to make 12.

Answer
4.

Reasoning
For each row, the left minus the right gives a number.

The numbers for the rows are then multiplied together.

In the first box:

   7 − 3 = 4
   4 − 1 = 3

so 4 x 3 = 12

In the second box:

   9 − 2 = 7
   8 − 3 = 5

so 7 x 5 = 35

In the last box:

   6 − 2 = 4
   8 − 7 = 1

so 4 x 1 = 4.