in favour of是赞成同意
do a favour for sb=do sb a favor是帮助,帮忙之意,所以
if you can do a favour for him=if you can do him a favour
不能用in favour of
in favour of是赞成同意
do a favour for sb=do sb a favor是帮助,帮忙之意,所以
if you can do a favour for him=if you can do him a favour
不能用in favour of