When a number is divided by 27, the quotient and remainder are both 15. What is this number?
一个数除以27，商和余数都是15，这个数是多少？
<gadget id="calculator">27 * 15</gadget>
<output>405</output>

<gadget id="calculator">405 + 15</gadget>
<output>420</output>

<result>420</result>