First you would have to isolate y.
3x - 3y = 18 -----> Subtract 3x from both sides
-3y = -3x + 18 --------> Now divide both sides by -3
y= x - 6
Now you replace the y with an f(x)
f(x) = x - 6
11.) 1.5
12.)17 1/2
13.)543
533+10
( Just remember absolute value.)
14.)$ 75.15
I hope this helps you
x+11=5x-5
4x=16
x=4