-4/5*3 7/9:(-2 3/7)*5 7/8:(-6 5/7)=- 4/5*34/7:17/7*47/8:47/7=
=- 4/5*34/7*7/17*47/8*7/47=- 4/5*34/1*1/17*1/8*7/1=- 4/5*2/1*1/1*1/8*7/1=
=- 4/5*2*1/8*7=-56/40=-14/10=-1,4
-42*5 1/4:3 3/8:(-2 4/5)*(-3 3/8)=-42*5 1/4:(2 4/5)=-42*21/4:14/5=-21*21/2*5/14=
=-3*21/2*5/2=-315/4=-78,75