Mike spent 37 dollars on notebooks.  He bought a total of 12 notebooks.  He bought 3 red notebooks at 4 dollars each, 2 green notebooks at 2 dollars each, and the rest were blue notebooks.  How much does each blue notebook cost?
He bought 12-3-2=
<gadget id="calculator">12-3-2</gadget>
<output>7</output>
7 blue notebooks.
He paid 3*$4=$
<gadget id="calculator">3*4</gadget>
<output>12</output>
12 for red notebooks.
He paid 2*$2=$
<gadget id="calculator">2*2</gadget>
<output>4</output>
4 for green notebooks.
He spent $37-$12-$4=$
<gadget id="calculator">37-12-4</gadget>
<output>21</output>
21 on blue notebooks.
Each blue notebook costs $21/7=$
<gadget id="calculator">21/7</gadget>
<output>3</output>
3.

<result>3</result>