Shengli Primary School has prepared 28 rows of seats for parents, with 9 seats in each row, but 36 seats were vacant during the parent-teacher meeting. How many parents are there in total?
胜利小学为家长准备了座位28排，每排9个，但开家长会时有36个座位空着．一共有多少家长来参加家长会？
<gadget id="calculator">9 * 28</gadget>
<output>252</output>

<gadget id="calculator">252 - 36</gadget>
<output>216</output>

<result>216</result>