The sum of 8.7 and 7.8 is 1.4 more than a number. Find this number.
8.7与7.8的和比一个数多1.4，求这个数．
<gadget id="calculator">7.8 - 1.4</gadget>
<output>6.4</output>

<gadget id="calculator">8.7 + 6.4</gadget>
<output>15.1</output>

<result>15.1</result>