Answer: Christina's age is 13, Joanne's age is 42 and Devin's age is 21.
Step-by-step explanation: If Devin's age is represented by d, then Joanne's age will be 2d because Joanne is two times Devin's age. Also, if Devin is 8 years older than Christina, then Christina's age would be d - 8. If the sum of their ages is equal to 76, then;
2d + d + (d - 8) = 76
2d + d + d - 8 = 76
4d - 8 = 76
Add 8 to both sides of the equation
4d = 84
Divide both sides of the equation by 4
d = 21
Therefore, Devin is 21 years old
Joanne is 42 years old and
Christina is 13 years old.