Elana mixes the tootpastes in large tanks in her basement after school. Both flavors are made from only four ingredients, which well call A, B, C, and D to preserve Elanas trade secrets. Ingredients A, B, and D are pumped into Tank 1 and mixed to make Candy Madness, which requires 2 gallons of B and 3 gallons of D for every gallon of A. Two-thirds of this mixture are drained and packaged, but one-third is pumped into Tank 2 where it is mixed with other ingredients to make Maple Sugar Supreme. This second recipe requires three times the amount of A used in Candy Madness, and it is flavored with 2 gallons of C for every 3 gallons of A.
If Elanas process produces 21 gallons of Maple Sugar Supreme per hour, how many gallons of Candy Madness are produced per hour?