a/b = 7/15 a = 7b/15
b/c = 3/8 c = 8b/3
a) (a+b)² = (7b/15 + b)² = (22b/15)² = 484b²/225
a² + 2ab + b² = 49b² /225 + 14b² /15 + b² = 484b² /225 ⇒
⇒ (a+b)² = a² + 2ab + b²
b) b - a = b - 7b/15 = 8b/15
5(b-a) = 8b/3 = c
c) a+b+c = 124
7b/15 + b +8b/3 = 62b/15 = 124 b/15 = 2 b = 30 a = 14 c = 80