y1=(80%(x-10)+10)*225,y2=90%x*225
y1=225x+(x-10)*0.8*225,(x>10)y1=225x (0y2=0.9*225x
设y=kx+b(k≠0)Y1=225(x-10)×80%=180x-1800(x≥10)Y2=90%x