（8分之7加16分之13）除以16分之9
=（7/8+13/16）x16/9
=(14/16+13/16)x16/9
=27/16x16/9
=3
5分之3加4分之3除以5分之3
=3/5+5/4
=12/20+25/20
=37/20
13分之7除以7加7分之1乘13分之5
=7/13x1/7+1/7x5/13
=(7/13+5/13)x1/7
=12/13x1/7
=12/91