Suppose initially you have $$500$ in cash $($and nothing else$).$

Now you purchase $2$ assets: a stock for $$280$ and a put on the stock for $$20(=$ the put premium$).$

At maturity of the option the stock trades at $$200$ and your account value is $$450.$

What was the strike price of the put $($assume you earn $0$ interest on cash$)?$