There are seven numbers, the average of these numbers is 49, the average of the first four numbers is 28, and the average of the last four numbers is 60, then what is the fourth number?
有七个数，这些数的平均数是49，其中前四个数的平均数是28，后四个数的平均数是60，那么第四个数是多少？
<gadget id="calculator">28 * 4</gadget>
<output>112</output>

<gadget id="calculator">60 * 4</gadget>
<output>240</output>

<gadget id="calculator">49 * 7</gadget>
<output>343</output>

<gadget id="calculator">240 - 343</gadget>
<output>-103</output>

<gadget id="calculator">112 + (-103)</gadget>
<output>9</output>

<result>9</result>