Seven numbers are arranged in a row, the average of the first 4 numbers is 43, and the average of the last 4 numbers is 72. Given that the average of seven numbers is 56, find the fourth number.
七个数排成一列，前4个数的平均数是43，后4个数的平均数是72．已知七个数的平均数是56，求第四个数是多少．
<gadget id="calculator">43 * 4</gadget>
<output>172</output>

<gadget id="calculator">72 * 4</gadget>
<output>288</output>

<gadget id="calculator">172 + 288</gadget>
<output>460</output>

<gadget id="calculator">56 * 7</gadget>
<output>392</output>

<gadget id="calculator">460 - 392</gadget>
<output>68</output>

<result>68</result>