The average of four numbers is 18, if each number is increased by x, what is the sum of these four numbers.
四个数的平均数是18，如果每个数都增加x，这四个数的和是多少．
<gadget id="calculator">18 * 4</gadget>
<output>72</output>

<gadget id="calculator">72 + 4</gadget>
<output>76</output>

<result>76</result>