Question

The sponsors of the marching band provided 128 sandwiches for a picnic. After the picnic, s sandwich’s are left.

Answer 1

A. 128-x=s ( x would be the sandwiches handed out and since we dont have a value we cant know exactly what the value is)

B . 128-x=15 so this means there were 113 sandwiches handed out 
(subtract 15 from 128 and you get the value of sandwiches handed out) 
Make sense? Hope i helped :)