Answer:
x - 6 = 15
Craig is 21 years old
Explanation:
x = Craig's age, 15 = Sue's age, and Sue is 6 years younger than Craig, so 15 (Sue's age) is 6 (Years) less than x (Craig's age). The equation is
x - 6 = 15
Using this, x - 6 = 15, we can add 6 to both sides to get x = 21, Craig is 21 years old