Consider:

$($a$)$ Stock trades for $$100$;

$($b$)$ Puts with exercise prices of $$90,$ $$100,$ and $$110$ trade at prices of $$4\mathrm{.}09,$ $$8\mathrm{.}68,$ and $$14\mathrm{.}24$ respectively.

If a person buys a $$110$ put and writes a $$90$ put, what is her maximum profit? Please answer correctly up to two decimal places.