Answer:
of water must be added.
Step-by-step explanation:
Given : The total quantity of mixture = 5 quarts
The percentage of acid= 0.40
Then, total liters of acid is given by :-

The amount of water in the given mixture : 
The percentage of acid in in weakened mixture = 0.30
Then , the percentage of water in weakened mixture = 0.70
Let 'x' amount of water is added to mixture.
Then According to the question ,we have the following equation :-

Hence,
of water must be added.