x+y=450(1)60%x-40%y=30(2)60x-40y=30003x-2y=150(3)2x+2y=900(4)(3)+(4) 5x=1050x=210y=450-x=450-210=240x=210y=240(2) 2x+2y=1(1)x-6y=1(2)2x-12y=2(3)(1)-(30 14y=-1y=-1/14x=1+6y=1-3/7=4/7x=4/7,y=-1/14我要详细的过程