The average of 6 numbers is 15, if one of the numbers is changed to 5, then the average of 6 numbers is 12. What is the original number that was changed?
有6个数的平均数是15，如果把其中一个数改为5，这时6个数的平均数是12．求这个被改动的数原来是多少？
<gadget id="calculator">15 * 6</gadget>
<output>90</output>

<gadget id="calculator">12 * 6</gadget>
<output>72</output>

<gadget id="calculator">90 - 72</gadget>
<output>18</output>

<gadget id="calculator">5 + 18</gadget>
<output>23</output>

<result>23</result>