|__|__|__|__|__|__|__|__|__|__|=>x=distanta totala a drumului
\---------------/=>4/10(x)
4/10(x)+20=1/2(x)......=>...1/2(x)=5/10(x)
20=1/10(x)....=> 4/10(x)+1/10(x)=5/10(x)
5/10(x)=4*20+1*20
=80+20
=100m......=>1/2(x)=100m
x=100*2
=200m ....=> distanta intre casa Irinei si biblioteca =200m