Mumford Corporation invested $30,000 in marketable securities on December 4. On December 9, it sold some of these investments for $10,000, and on December 18, it sold more of these investments for $5,000. The securities sold on December 9 had cost the company $7,000, whereas the securities sold on December 18 had cost the company $6,000. record the purchase of marketable securities on December 4.