7.86-(5.63-0.86)-1.73
=7.86+0.86-5.63-1.73
=8.72-(5.63+1.73)
=8.72 -7
=1.72
(1÷0.5+0.5÷1)÷5.1
=(2+0.5)÷5.1
=2.5÷5.1
=25/51