A jar contains 9 blue pens, 21 black pens, and 6 red pens. Four blue pens are removed and then seven black pens are removed. How many pens are left in the jar?
There are 9-4 = 
<gadget id="calculator">9-4</gadget>
<output>5</output>
5 blue pens left in the jar.
There are 21-7 = 
<gadget id="calculator">21-7</gadget>
<output>14</output>
14 black pens left in the jar.
There are 5+14+6 = 
<gadget id="calculator">5+14+6</gadget>
<output>25</output>
25 pens left in the jar.

<result>25</result>