Ответ:
4(30-2у)-у(30-2у)=0
4*30-4*2y-y30+y*2y=0
120-8y-30y+2y^2=0
120=8y+30y+2y^2
120=38y+2y^2
120=(38+2+1)*y
120=41y
y=120/41