The average of three numbers is 3.6. If 3 is added, what is the average of these four numbers?
三个数的平均数是3.6，如果再加上3，那么这四个数的平均数是多少．
<gadget id="calculator">3.6 * 3</gadget>
<output>10.8</output>

<gadget id="calculator">10.8 + 3</gadget>
<output>13.8</output>

<gadget id="calculator">13.8 / 4</gadget>
<output>3.45</output>

<result>3.45</result>