15/x + 15/y = 1/6 12/x + 20/y = 1/5 1/x+1/y=1/900.6/x+1/y=1/1000.4/x=1/900x=3601/y=1/90-1/360=1/120y=120
x=360,y=120令1/x=a,1/y=b,得，a,b然后得x,y
x=360y=120
