What do u add to 3 and 3 / 8 to make 7

Aformual for 8 bottles of window cleaner calls for 6 cups of rubbing to customers alcohol 2 1/4 gallons of water and 1 1/2 cups of ammonia alcohol would the forula call if a factory made 1,280 bottles for stores to sell to customers

What’s the answer ? use the picture to see the problem

What is the slope of the line that has an equation of y equals x -3