The gymnasium is playing table tennis singles and doubles. There are 4 more players in the doubles than in the singles. There are 13 table tennis tables for the game. How many players are there in the doubles?
体育馆正在进行乒乓球单打、双打比赛，双打比赛的运动员比单打的运动员多4名，比赛的乒乓球台共有13张，那么双打比赛的运动员有多少名．
<gadget id="calculator">30 / 6</gadget>
<output>5</output>

<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>