How to find the missing number

Question

How to find the missing number

$\{14,36,25,25\},\{20,50,20,10\},\{36,54,7,?\}$

answer was $3$ , but I dont understand why?

well these four sets of numbers were kept in four seperate circular plate and the plates were divided in four part.

Answer 1

Hint: What is the sum of the elements in the first set? What about the second set?

Answer 2

Answer is 3 , Sum of each set is equal to 100 so in the last set if we add 3 the sum becomes 100