Răspuns :
a + b + c = 90
a = 2b + 5
c = 4b + 10 + 5
2b + 5 + b + 4b + 10 + 5 = 90
7b + 20 = 90
7b = 90 - 20
7b = 70
b = 70 : 7
b = 10
a = 2 × 10 + 5
a = 25
c = 2 × 25 + 5
c = 55
a = 2b + 5
c = 4b + 10 + 5
2b + 5 + b + 4b + 10 + 5 = 90
7b + 20 = 90
7b = 90 - 20
7b = 70
b = 70 : 7
b = 10
a = 2 × 10 + 5
a = 25
c = 2 × 25 + 5
c = 55