需要加水x千克
(18*95%)/(18*95%+x)=75%
17.1=17.1*0.75+0.75x
0.75x=17.1*0.25
x=5.7......错了吧改正后需要加水x千克(18*95%)/(18+x)=75%17.1=18*0.75+0.75x0.75x=17.1-13.5x=4.8