Client was issued a W2 with and amount on Box 12V for $105,000.  Client was also issued a 1099B with proceeds listed at $116,000 and "Unknown" Cost Basis. Looking over the supplements there were two transaction in the year. One in the amount of $42,000 that list the cost basis of $42,000.  The second in the amount of $74,000 that does not list the cost basis, its blank.

When entering the information on Schedule D do I use the amount on Box 12V of the W2 as the cost basis?  Is the gain the difference between the $105,000 and $116,000?