The average of the four numbers is 12.5, if each number is increased by b, what is the sum of these four numbers.
四个数的平均数是12.5，如果每个数增加b，那么这四个数的和是多少．
<gadget id="calculator">12.5 * 4</gadget>
<output>50</output>

<gadget id="calculator">50 + 4</gadget>
<output>54</output>

<result>54</result>