Answer:
$7,500
Step-by-step explanation:
According to the IRS publication 541, if any property is contributed to the partnership in exchange for an interest in the partnership, neither the partner nor the partnership will recognize any gain or loss. This applies to forming partnerships or already operating partnerships.
The partner's basis and holding period will be passed to the partnership. In this case, ABCD's basis in the land is $7,500 (Billy's basis).