It took 7 1/4 gallons of gas tofill the tank of the family car. This is 3/4 of the amount the tank can hold. How much gas does the tank hold?

Let C equal the capacity of the tank. If 3/4 of C is 7 1/4 gallons, then you have the equation:

3/4 C = 7 1/4

I suggest changing the mixed fraction 7 1/4 to a simple fraction of 29/4:

3/4 C = 29/4

Solve for C.