The school organized a donation activity. Xiaotong donated 18.2 yuan, Xiaohua donated 2.2 yuan more than Xiaohua, and He Lan donated 3.7 yuan less than Xiaohua. How much did He Lan donate?
学校组织捐款活动，小童捐了18.2元，晓华捐的钱比小童多2.2元，何兰捐的钱比晓华少3.7元．何兰捐了多少钱？
<gadget id="calculator">21 - 3.7</gadget>
<output>17.3</output>

<result>17.3</result>