13/14-15/28÷5/8
=13/14-15/28*8/5
=13/14-15*8/(28*5)
=13/14-3*4/14
=1/14
(5/6-3/4)÷3/8
=1/12*8/3
=2/9
5/9*5/6+4/9÷6/5
=25/ 54+20/54
=5/6
4÷4/5-4/5÷4 7/11÷
=5-4/5*11/47/(2/5*3/10)
=5-4*11/(5*47)*25/3
=5-4*11*25/(5*4*3)
=5-11*5/3
=5-18又1/3
=13又1/3.