DM Company's assets are expected to increase from $25,000 in 2007 to $45,000 in 2012, while their accounts payable are expected to increase by $9,500 in 2008. The company is also expected to repay $7,000 on an outstanding loan during 2012, and their NIAT is expected to be $2,500. The company does not pay dividends. What is the amount of external financing the company requires?
A.$17,500
B.$20,000
C.$15,000
D.$29,000
and why.