Mrs. Park has 3 boxes of crayons. Each box has 12 crayons. Mrs. Park takes c crayons out of each box. Which expression can be used to find the total number of crayons left in these boxes?

Ahousekeeper mixed 5 gallons of blue paint with every 9 gallon of yellow paint in order to make a green paint which ratio of gallon of blue paint to gallon of yellow paint will make the same shade of green paint