Question 76007
Let z = Zel's age now; Let s = son's age now
:
"Zelma is 18 years older than her son." says:
z = (s + 18)
or
s = (z - 18)
:
"She was 3 times as old as he was 1 year ago." says: 
(z-1) = 3(s-1)
z - 1 = 3s - 3
z = 3s - 3 + 1
z = 3s - 2
:
How old are they now?
:
Substitute (z-18) for s, in z = 3s - 2
z = 3(z-18) - 2
z = 3z - 54 - 2
z - 3z = -56
-2z = -56
z = -56/-2
z = +28 yrs old;  then s = 28 -18 = 10 yrs old
:
Check: 
(28-1) = 3(10-1)
 27 = 3(9)