Hello there. To solve this question, we'll have to remember some properties about ratio and areas.
Knowing the total square footage of wall space to be painted is 625 ft², we have to determine how many quarts of paint will be required for the project, if a gallon of paint covers 250 ft².
First, we have to remember that 1 gallon is the same as 4 quarts, therefore we can divide how many square feet the gallon covers with paint by 4 to find how many will one quart cover:

Now, we have to divide the total area to be covered by how many square feet one quart covers, to determine how many quarts will be needed:

Therefore, we need 10 quarts of paint for this project.