Răspuns:
a + b + c = 76
a + b = 42
c = 10 + a
a + b + 10 + a = 76
2a + b + 10 = 76
2a + b = 76 - 10
2a + b = 66
a + b = 42 / × (-1)
-1 × ( a + b ) = -1 × 42
- a - b = - 42
2a + b - a - b = 66 - 42
2a - a = 66 - 42
a = 24
24 + b = 42
b = 42 - 24 => b = 18
c = 10 + 24
c = 34
Verificare : 24 + 18 + 34 = 76