Given that

$$Totalvolume=25liters$$

$$Percentageofsolvent=40\mathrm{\%}$$

$$Percentageofwater=60\mathrm{\%}$$

So,

$$Volumeofsolvent=\frac{40}{100}\times 25$$

$$=10liters$$

$$Volumeofwater=\frac{60}{100}\times 25$$

$$=15liters$$

$$Literstoadd=15-10=5liters$$