The answer is 36.
The hidden logic involves adding the two numbers together and then multiplying that sum by the first number in the equation X × (X + Y).
Here is the pattern applied to each row:
1 + 2 = 3: 1 × (1 + 2) = 1 × 3 = 3
3 + 4 = 21: 3 × (3 + 4) = 3 × 7 = 21
5 + 6 = 55: 5 × (5 + 6) = 5 × 11 = 55
Following this exact rule for the final equation:
