let's break this statement down:

30 liters of a solution of water and acid contains 15% acid

In the phrase aforementioned, the amount of water is 30*0.85

If more water is added to change the solution

Let's define the amount of extra water as X

The amount of water in the final solution

Due to the fact that the final solution must be five percent acid, the amount of water in that mixture will be 0.95 percent. In addition, that solution has in total 30 liters and x liters. Therefore, the amount of water in the final solution must be:

0.95(30+x)

Finally, setting up the euation, we have:
Water in the initial mixture + additional water = amount of water in the final solution
\(30*0.85 + x = 0.95(30+x)\)
\(x = 60\)

However, 60 stands for the extra water. We need to figure out how much water was previously. The last, can be achieved by multiplying 30*0.85 = 25.5, and adding 60. Therefore, the total amount of water is 60 + 25.5 = 85.5.

Option D.