A=4/5-(7/10-5/6)
=4/5-(41/60-50/60)
=4/5-(-8/60)
=4/5+8/60
=48/60+8/60
=56/60=14/15
B=3/18+5/11×77/15
=3/18+385/165
=3/18+7/3
=3/18+42/18
=45/18=5/2
C=5/9÷(5/9+1/6)
=5/9÷(30/54+9/54)
=5/9÷39/54
=5/9÷13/18
=5/9×18/13
=5×2/13
=10/13
