Billy owns Billy's Balloons $($BB$),$ a company that provides balloons for corporate events and large parties. BB agreed in writing with Corporate Promotions $($CP$)$ to hold the price of $$3,000$ for $10,00018-$inch diameter helium balloons open for $CP$ for the next two months. $CP$ paid nothing additional to BB for the right to pay this price over the next two months. Which of the following is this agreement known as and is it a valid contract?

Multiple Choice

This is a merchant's firm offer but it is not valid because CP paid no consideration for it$.$

This is a merchant's firm offer but it is not valid because it is for longer than the $30-$day limit on such offers.

This is a merchant's firm offer and it is valid.

This is a common law unilateral contract offer and it is valid.