Dave was at risk for $25,000 in Partnership X and $25,000 in Partnership Z on January 1, 2013. Both partnerships are passive activities to Dave (these are Dave's only passive activities). Dave's share of net income from Partnership X during 2013 is $15,000. Dave's share of losses from Partnership Z during 2013 is $50,000. How much is Dave at risk for Partnership X on January 1, 2014?
a. $0
b. $15,000
c. $25,000
d. $40,000