(40x3/8-6)÷3/7=(15-6)x7/3=9x7/3=3x7=21
100x1/4=25
21:25
(5/6+1/9÷1/3)÷7/8=(5/6+1/9x3)x8/7=(5/6+1/3)x8/7=(5/6+2/6)x8/7=7/6x8/7=8/6=4/3