The sum of 3.9 times of a number and its 2.5 times is 80, what is this number?
一个数的3.9倍与它的2.5倍的和是80，这个数是多少？
<gadget id="calculator">3.9 + 2.5</gadget>
<output>6.4</output>

<gadget id="calculator">80 / 6.4</gadget>
<output>12.5</output>

<result>12.5</result>