x = y + 20
x - 4 = 3 * ( y - 4)
y + 20 - 4 = 3*y - 3*4
y+16 = 3*y - 12
16 + 12 = 3*y - y
28 = 2*y
y = 28 : 2
y = 14
x = 14 + 20
x = 34
x = varsta mamei, y = varsta fetei * = inmultire
Mama 34 ani, fiica 14 ani
Verificare: 34 - 14 = 20
(34 - 4) : ( 14 - 4 ) = 30 : 10 = 3