2015 Cayley Problem 19

A bank teller has some stacks of bills. The total value of the bills in each stack is \$1000. Every stack contains at least one \$20 bill, at least one \$50 bill, and no other types of bills. If no two stacks have the same number of \$20 bills, what is the maximum possible number of stacks that the teller could have?

\textbf{(A)}\ 9\quad \textbf{(B)}\ 10\quad \textbf{(C)}\ 11\quad \textbf{(D)}\ 4\quad \textbf{(E)}\ 8

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Cayley contests here.