x - 4 = Jill's age 4 years ago
x + 2 = Jack's age 4 years ago {subtracted 4 from x + 6}
2(x - 4) - 3 = x + 2 {four years ago, Jack's age was equal to 3 years less than twice Jill's age}
2x - 8 - 3 = x + 2 {used distributive property}
2x - 11 = x + 2 {combined like terms}
x = 13 {subtracted x and added 11 to each side}