The Ricco family filled the gasoline tank of their car at the beginning of a long trip. Their car used gasoline at the rate of 1 gallon every 21 miles. When they stopped for lunch, they had driven 315 miles, and there were 9 gallons of gasoline left in the tank. How many gallons does the gasoline tank hold?

x - 315/21 = 9

Solve for x.

24 gallons

To determine the capacity of the gasoline tank, we need to find the total amount of gasoline used during the trip and add it to the amount remaining.

First, let's calculate the amount of gasoline used to drive 315 miles. We know that the car uses 1 gallon of gasoline for every 21 miles. Therefore, for 315 miles, the car would have used:

315 miles / 21 miles/gallon = 15 gallons

Now let's add the amount of gasoline remaining (9 gallons) to the amount used (15 gallons):

15 gallons + 9 gallons = 24 gallons

Therefore, the gasoline tank holds 24 gallons.