PLEASE HELP,URGENT!!!GMAT PREP Q

[blkcactus]

Hey guys, it might seem like an easy question to you but I am really confused as to how to get the answer without calulating the value of each exponantial.. :( Could someone please help me out on this? it is kinda urgent since im taking the test morro :( THANK YOUUU

What is the greatest prime factor of 2^100 - 2^96?

A. 2
B. 3
C. 5
D. 7
E. 11

[whoops]

Hey guys, it might seem like an easy question to you but I am really confused as to how to get the answer without calulating the value of each exponantial.. :( Could someone please help me out on this? it is kinda urgent since im taking the test morro :( THANK YOUUU

What is the greatest prime factor of 2^100 - 2^96?

A. 2
B. 3
C. 5
D. 7
E. 11

2^100 - 2^96
=2^96*2^4 - 2^96
=2^96(2^4-1)
=2^96*15

15=3*5
the greatest prime factor of 2^100 - 2^96 is 5