A Mixture of 6 Gallons of Chemical A, 7 Gallons $Y$

A mixture of 6 gallons of chemical A, 7 gallons of chemical B, and 10 gallons of chemical C is required to kill a crop destroying insect. Commercial spray X contains 1, 2, and 3 parts of these chemicals, respectively. Commercial spray Y contains only chemical C. Commercial spray Z contains chemicals A, B, and C in equal amounts. How much of commercial spray $Y$ is needed to obtain the desired mixture?

A) 14 gallons
B) 1 gallon
C) 16 gallons
D) 2 gallons
E) 6 gallons