四分之七乘以四分之三除以八分之八，十三乘以八分之九除以(六分之五減去四分之三)。

=7/4*1/18+7/4*3/8

=31/72*7/4

=217/288

13/8*[(8/9)/(5/6-3/4)]

=13/8*(8/9)/(1/12)

=52/3

5/12*1/13-(1/4)/13

=5/12*1/13-1/52

=2/156

=1/78