Fie m- varsta mamei
f- varsta fiului
m-8=15*(f-8)
m-8=15f-120
m=15f-120+8
m=15f-112
m+10=f+10+28
m=f+10+28-10
m=f+28
15f-112=f+28
15f-f=28+112
14f=140
f=140:14
f=10
m=10+28=38
Verificare:
38-8=15*(10-8)
30=30 (adevarat)
38+10=10+10+28
48=48 (adevarat)