Answer:
25
Step-by-step explanation:
For each problem, the two numbers on the left are perfect squares. The number in the upper right is the square of the difference between the two numbers on the left. The number on the bottom right is equal to the number on the upper right plus the number on the upper left.
For problem 16, we know that the square of the difference between 36 and the missing number is 121. The square root of 121 is 11, so the missing number is 36 - 11 = 25 which fits the pattern because it is also a perfect square.
(Also if you look at problem 15, it basically gives you the answer to problem 16.)
