7/12-3/7）-(4/7-7/12）=7/12+7/12-3/7-4/7=14/12-1=2/12=1/6
5/7+19/25*4+21/25*199=5/7+(1-6/25)x4+(1-4/25)x199
=5/7+4-24/25+199-4x(200-1)/25
=5/7+203-24/25-32+4/25
=171+5/7-4/5
=171+25/35-28/35
=171-3/35
=5982/35
43/73*67+69*26/73
=(43x67+69x26)/73
=(2881+1794)/73
=4675/73