Marianne was 20 years old when Bella was 8 years old. How old will Marianne be when Bella turns 18? Let's answer step by step:
Marianne is 20 - 8 = 12 years older than Bella. Bella will turn 18 in 18 - 8 = 10 years. So, Marianne will be 20 + 10 = 30 years old then. The answer: 30.