The function 6(n)=14n represents the number of baseballs b(n) that are needed for n games. How many baseballs are needed for 21 games?

A. 35
B. 7
C. 294
D. 120

To find how many baseballs are needed for 21 games, we substitute 21 for n in the expression 6(n)=14n. We have 6(21)=14(21), which simplifies to 126=294. Thus, the answer is $\boxed{\textbf{(C) }294}$.