Question: I would love to understand how to solve this problem: Alice is 7 years older than Beth, who is 5 years older than Erica. What is the difference between the ages of Alice and Erica, if Erica is 30 years old?
Can you explain?
Answer: 
Beth is 30+5 = 35 years old.
Alice is 35+7 = 42 years old.
The difference between the ages of Alice and Erica is 42-30 = 12 years.