Răspuns :
a + b = 25
b = 4a
a + 4a = 25
5a = 25
a = 25 : 5
a = 5
b = 4x5
b = 20
verificam
5 + 20 = 25
b = 4a
a + 4a = 25
5a = 25
a = 25 : 5
a = 5
b = 4x5
b = 20
verificam
5 + 20 = 25