Use reasoning to lead to the answer of the following question:
Marianne was 20 years old when Bella was 8 years old. How old will Marianne be when Bella turns 18?

30
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.

.

Therefore, the answer is 30