Carlos has a basis in his partnership interest of $30,000. He receives a current distribution of $6,000 cash, unrealized receivables (FMV $11,000, basis $10,000), inventory (FMV $8,000, basis $4,000), land held as an investment (FMV $7,000, basis, $6,000), and building (FMV $21,000, basis $9,000). The partners' relative interests in the Sec. 751 assets do not change as a result of the current distribution. Carlos's basis in the building is