Let
f(x) = 4x + 1 if x <=3
f(x) = 18 - 4x if x > 3
Find the sum of all values of x such that f(x) = 0.
Set each part = 0 and solve
4x+1 = 0
4x = - 1
x = - 1/4 which is <= 3 so it is a valid answer
18 - 4x = 0
- 4x = -18
x = 18/4 = 4 1/2 which is >3 so it is a valid answer too
Add 'em together.....