a + b + c = 515
a + m = 134 ==> a = 134 - m
b + m = 186 ==> b = 186 - m
c + m = 225 ==> c = 225 - m
134 - m + 186 - m + 225 - m = 515
3 × m = 545 - 515
3 × m = 30
m = 30 : 3
m = 10
a = 134 - 10 = 124
b = 186 - 10 = 176
c = 225 - 10 = 215
Verificare:
124 + 176 + 215 = 515