The average of seven numbers is 62. If one of the numbers is changed to 90, the average is 74. What is the original number?
七个数的平均数是62，把其中一个数改为90，平均值为74，这个数原来是多少．
<gadget id="calculator">74 * 7</gadget>
<output>518</output>

<gadget id="calculator">62 * 7</gadget>
<output>434</output>

<gadget id="calculator">518 - 434</gadget>
<output>84</output>

<gadget id="calculator">90 - 84</gadget>
<output>6</output>

<result>6</result>