Jenny bought 6 cookies and 6 cupcakes at the bakery. The cookies were $1.50 each, but she cannot remember how much each cupcake was. She paid $21 total. How much was each cupcake?

The total cost of the cookies is 6 * 1.50 = $<<6*1.50=9>>9.

So, Jenny paid 21 - 9 = $<<21-9=12>>12 for the cupcakes.
Thus, each cupcake cost 12/6 = $<<12/6=2>>2. Answer: \boxed{2}.