3/8x[8/9÷(5/6一3/4)]=3/8x8/9÷(5/6一3/4)=1/3÷1/12=4
3/8x[8/9÷(5/6-3/4)]=3/8×[8/9÷1/12]=3/8×8/9÷1/12=1/3×12=4