87*79-79*77 (simple algorithm)
87*79-79*77(简便算法)
<gadget id="calculator">87 * 79</gadget>
<output>6_873</output>

<gadget id="calculator">79 * 77</gadget>
<output>6_083</output>

<gadget id="calculator">6_873 - 6_083</gadget>
<output>790</output>

<result>790</result>