What is the difference between 30 minus the product of 3.9 times 5?
30减去3.9乘以5的积，差是多少？
<gadget id="calculator">3.9 * 5</gadget>
<output>19.5</output>

<gadget id="calculator">30 - 19.5</gadget>
<output>10.5</output>

<result>10.5</result>