It takes Xiao Ming 5 minutes to wash up in the morning, 6 minutes to boil water, and 15 minutes to review homework. How many minutes does it take him at least to complete these three things?
小明同学早上起来洗漱要用5分钟，煮开水要用6分钟，温习功课要用15分钟，完成这三件事，他最少要用多少分钟
<gadget id="calculator">15 - 6</gadget>
<output>9</output>

<gadget id="calculator">5 + 6 + 9</gadget>
<output>20</output>

<result>20</result>