The average of three numbers is 1.8, what is the average of these four numbers if 1 is added
三个数得平均数是1.8，如果再加上1，这四个数的平均数是多少
<gadget id="calculator">1.8 * 3</gadget>
<output>5.4</output>

<gadget id="calculator">5.4 + 1</gadget>
<output>6.4</output>

<gadget id="calculator">6.4 / 4</gadget>
<output>1.6</output>

<result>1.6</result>