Answer: There are 11 gallons which will be used by him to paint the inside of his barn.
Explanation:
Since we have given that
Total number of quarts he needed in all =107
Let the number of quarts he needed for the inside of his barn be x
Let the number of quarts he needed for the outside of his barn be x+19
According to question,

As we know that

So, there are 11 gallons which will be used by him to paint the inside of his barn.