（6.9乘0.25乘1.75）除以（2.3乘八分之一乘四分之一）

(6.9*0.25*1.75)=6.9*(1/4)*(7/4）
(6.9*0.25*1.75)/[2.3*(1/8）*(1/4)]
＝[6.9*(1/4)*(7/4)]/[2.3*(1/8）*(1/4)]
=(6.9/2.3)*[(1/4)/(1/4)]*[(7/4)/(1/8)]
=3*1*14
=42