Here’s a possible solution:
Note the pattern:
(no. on the left) x (sum of both numbers) = Answer.
That is,
(a) For 1 + 2, we have
1 x (1 + 2) = 1 x 3 = 3
(b) For 3 + 4, we have
3 x (3 + 4) = 3 x 7 = 21
(c) For 5 + 6, we have
5 x (5 + 6) = 5 x 11 = 55
So, 4 + 5 equals
4 x (4 + 5) = 4 x 9 = 36
Thus, Answer = 36
