Question 964874
Let the sisters ages be (x-2),x and (x+2)
where (x-2) is the younger sister's age
        x   is the middle sister's age
      (x+2) is the elder sister's age
Seven more than the youngest sister's age is eight less than twice the oldest sister's age.
(x-2)+7=2(x+2)-8
x+5=2x-4
2x-x=5+4
x=9
The middle sister is 9 years old.
The younger sister is 7 years old.
The elder sister is 11 years old.