270(x+15)-300x=x(x+15)
270X+4050-300X=X^2+15X
X^2+45X-4050=0
(X+90)(X-45)=0
X=-90或X=45
960(x+20)-960x=4x(x+20)
960X+19200-960X=4X^2+80X
4X^2+80X-19200=0
X^2+20X-4800=0
(X+80)(X-60)=0
X=-80或X=60