First, we should assign variables.
Sandra’s Age = X + 18
Paolo’s Age = X
In 13 years, they will be:
(X + 18) + 13 = 2(x + 13)
X + 18 + 13 = 2x + 26
X + 31 = 2x + 26
X – 2x = 26 - 31
-x/-1 = -5/-1
X = 5
Therefore, Sandra is now:
Sandra’s Age = 5 + 18 = 23
Sandra is now 23 years old.
Checking their age:
23 (Sandra) – 5 (Paolo) = 18