Kelly's sister is x years old.
Kelly is 3 years younger than her sister, so Kelly is x - 3 years old.
The sum of their ages is x + x - 3 = 2x - 3.
The sum of their ages is 34, so
2x - 3 = 34
2x = 37
x = 18.5 Kelly's sister's age.
x - 3 = 18.5 - 3 = 15.5 Kelly's age.
Kelly's sister is 18.5 years old.
Kelly is 15.5 years old.
