Five numbers are arranged in a row, and the average number is 9. If the average number of the first four numbers is 7, and the average number of the last four numbers is 10, what is the average number of the first number and the fifth number?
五个数排一排，平均数是9，如果前四个数的平均数是7，后四个数的平均数是10，那么，第一个数和第五个数的平均数是多少？
<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<gadget id="calculator">7 * 4</gadget>
<output>28</output>

<gadget id="calculator">45 - 28</gadget>
<output>17</output>

<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<gadget id="calculator">45 - 40</gadget>
<output>5</output>

<gadget id="calculator">17 + 5</gadget>
<output>22</output>

<gadget id="calculator">22 / 2</gadget>
<output>11</output>

<result>11</result>