The elder brother and the younger sister set off from home to the exhibition hall by bicycle at the same time. The younger sister’s speed was half that of the older brother. After 30 minutes of departure, the older brother remembered that he didn’t bring his camera, so he went home immediately to get it. The older brother got the camera and chased after the younger sister. How many minutes did it take from when the elder brother got the camera to when he caught up with the younger sister?
哥哥和妹妹同时从家骑车出发去展览馆，妹妹的速度是哥哥的一半，出发30分钟后，哥哥想起没带相机，便立即回家去取，哥哥拿到相机再去追妹妹．从哥哥拿到相机到他追上妹妹用多少分钟．
<gadget id="calculator">2 - 1</gadget>
<output>1</output>

<gadget id="calculator">2 / 1</gadget>
<output>2</output>

<gadget id="calculator">1 * 30 * 2</gadget>
<output>60</output>

<result>60</result>