6/7+3/4*12/7
=6/7(1+3/4 *2)=6/7(1+3/2)=6/7*5/2=15/7
5/3*7/8-7/8*2/3=7/8(5/3-2/3)=7/8
2/3*45*1/10=2/3*9*5*1/10=3*2*5*1/10=3