Lets have the younger person be x.
The older person will be 8x + 3.
The sum of their ages is 21, so we can get this equation:
x + (8x+3) = 21
9x+3 = 21
Subtract 3 from both sides
9x = 21
x=3 --> The younger person is 3 years old, and now we can substitute that for the older person (8x+3):
(3 * 8) + 3 = 27
The younger person is 3 years old, and the older person is 27.
