My current age, is the age of my 14 year-old brother plus one third of my age. How old will I be when my brother is twice his current age?
I will be 35. I am currently 21.
x = my current age
x = 14 + x/3
3x = 42 + x
2x = 42
x = 21 (so 14 years later, I'll be 35)