A chemist needs to create a $50\%$ HCl solution. $($HCl is hydrochloric acid. A $"50\%$ HCl solution" contains $50\%$ HCl and the other $50\%$ is water.$)$

How much of a $72\mathrm{.}5\%$ HCl solution must be mixed with $30$ ml of a $15\%$ HCl solution in order to result in a $50\%$ HCl solution?

Round your answer to $2$ places after the decimal point $($if necessary$)$ and do NOT type any units $($such as $"$ml$")$ in the answer box.

Amount of $72\mathrm{.}5\%$ HCl solution:

ml