The students in Class 21 do morning exercises. The whole class is arranged in 4 rows, and the number of people in each row is equal. When Jiajia stands in a row, she is the 5th and the one from the back is the 1st. How many people are there in Class 21?
二1班同学做早操，全班排4列，每列人数相等，佳佳站在一列中前面数过去是第5个，从后面数过来是第1个，二1班一共有多少人．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>