At a restaurant each adult meal costs $2 and kids eat free. If a group of 15 people came in and 9 were kids, how much would it cost for the group to eat?
<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">2 * 6</gadget>
<output>12</output>

<result>12</result>