Answer:
b = S - a - c
Step-by-step explanation:
You just move every other term except for the one you're solving for to the other side, using the opposite operations
S = a + b + c
S - a = b + c
S - a - c = b
b = S - a - c
OR
S = a + b + c
-b + S = a + c
-b = -S + a + c
b = S - a - c (we flipped all signs here to make b positive, like it's supposed to be. The justification for this is multiplying both sides by -1)
