Question 714908
 Frank is 17 years old and his grandfather is 77 years old.
 How old will Frank's grandfather be when he is exactly 4 times as old as Frank?
:
Let y = the number years later for this to be true
77 + y = 4(17 + y) 
77 + y = 68 + 4y
77 - 68 = 4y - y
9 = 3y
y = 9/3
y = 3 yrs, when Grandpa will 4 times as old as Frank
:
At that time (add 3 to their ages), Grandpa will 80, and Frank will be 20