a+b=7 /×103
c-b=25 /×3
103a+103b=721
3c-3b=75 (+)
103a+100b+3c=721+75
103a+100b+3c=796
a + b = 7 => 103a + 103b = 7×103 = 721
c - b = 25 => 3c - 3b = 25×3 = 75
adunam relatiile
103a + 103b + 3c - 3b = 721 + 75
103a + 100b + 3c = 796
