Hello.
San is currently 5 years old.
Tom is currently 3 times older than San. This means that Tom is 15 years old (multiply San's age by 3 to distinguish this).
San is 5, and in 15 years, he will be 20. To simply put it, add 15 to Tom's age and we will know how old he will be when San is 20.
15 + 15 = 30
When San is 20, Tom will be 30 years old.
I hope this helps!
