Question 961974
w, amount of water to add, assuming as volume (liters)


{{{(0.35*0.15)/(0.35+w)=0.07}}}
Solve!


{{{0.07(w+0.35)=0.35*0.15}}}

{{{w+0.35=(35/7)(0.15)}}}

{{{w=-0.35+5*0.15}}}

{{{highlight(w=0.4)}}}