Răspuns :
a + b = 57
a = b + 13
b + 13 + b = 57
2b = 57 - 13
2b = 44
b = 44 : 2
b = 22
a = 22 + 13
a = 35
verificam
35 + 22 = 57
a = b + 13
b + 13 + b = 57
2b = 57 - 13
2b = 44
b = 44 : 2
b = 22
a = 22 + 13
a = 35
verificam
35 + 22 = 57