................................
a=copilul
b=mama
c=tata
a+b+c=84
b=ax4=>a=b/4
b=c-3=>c=3+b
b+b/4+3+b=84
b+b/4+b=81
4b+b+4b/4=81
9b=324=>b=36 ani
a=36:4=9 ani
c=36+3=39
