100 ---> 96 is -4
96 ---> 104 is +8
104 ---> 88 is -16
88 ---> 120 is +32
120 ---> 56 is -64
So first we go down by 4, then up by 8, then down 16, then up 32, then finally down 64.
The pattern of numbers is: -4, +8, -16, +32, -64
Notice it's the powers of 2:
2^2 = 4
2^3 = 8
2^4 = 16
2^5 = 32
2^6 = 64
each term doubles. Also each term alternates in sign. One is positive, then the next is negative and so on.
The last difference is -64, which doubles to -128. Change the sign to positive to get +128
Add 128 to the last term of 56 to get
128+56 = 184
Therefore, the final answer is 184