To find for the last sum of 16, 36, and 72, we need to decompose all prime factors such as shown below:
16=16,8,4,2,1
36=36,18,9,3,1
72=72, 36,18,9,3,1
x=64,32,16,8,4,2,1
The value of x is 128. Therefore, the answer to the last sum is 16, 36, 72, 128.