The average of the four numbers is 25, the average of the first three numbers is 24, what is the fourth number.
四个数的平均数是25，前三个数的平均数是24，第四个数是多少．
<gadget id="calculator">25 * 4</gadget>
<output>100</output>

<gadget id="calculator">24 * 3</gadget>
<output>72</output>

<gadget id="calculator">100 - 72</gadget>
<output>28</output>

<result>28</result>