x:(x-3)=7:57(x-3)=5x7x-21=5x2x=21x=10.5
5x=7(x-3)5x=7x-2121=7x-5x21=2xx=10.5
7x-21=5x(7-5)x=212x=21x=10.5
依题埋明中 得 X/(X-3)=7/5.于是 7×(弯山X-3)=5×X 于是 7X-21=5X 于槐滑是 X=10.5