You engage in the following strategy

$1.$Buy a put, strike price $=$ $$5,$ option premium $=$ $$2$;

$2.$Buy a put strike $=$ $$15,$ option premium $=$ $$4$;

$3.$sell two puts with a strike price $=$ $$10$; option premia $=$ $$2\mathrm{.}50$ each

All options written on $100$ shares.

Within $$10,$ what is the maximum possible gain?