Marianne was 20 years old when Bella was 8 years old. How old will Marianne be when Bella turns 18?
Marianne is 20 - 8 = <T>subtract(20, 8)=12 years older than Bella.
Bella will turn 18 in 18 - 8 = <T>subtract(18, 8)=10 years.
So, Marianne will be 20 + 10 = <T>add(20, 10)=30 years old then.
