Xiaowei did 25 math problems in 5 days. He did one more math problem every day than the previous day. Calculate how many problems he did in the last day.
小伟5天做了25道数学题，他每天都比前一天多做一道，算一算，他最后一天做了多少道题．
<gadget id="calculator">25 / 5</gadget>
<output>5</output>

<gadget id="calculator">5 + 2</gadget>
<output>7</output>

<result>7</result>