若是 5·(x-8)/8 = 30， x-8 = 30(8/5) = 48, x = 56.若是 5x(x-8)/8 = 30, x(x-8) = 48, x^2-8x-48 = 0, x = 12, -4
5*(x-8)=30*85x-40=2405x=280x=56
5x(x-8)=30*8=240x-8=240/5=48x=56
