2.5 times a number, plus the product of 4.5 times 6, the sum is 77, find this number.
一个数的2.5倍，加上4.5乘6的积，和是77，求这个数．
<gadget id="calculator">4.5 * 6</gadget>
<output>27</output>

<gadget id="calculator">77 - 27</gadget>
<output>50</output>

<gadget id="calculator">50 / 2.5</gadget>
<output>20</output>

<result>20</result>