When a number is divided by 3, the quotient is 15 and the remainder is 6. What is the number?
一个数除以3，商是15，余数是6，这个数是多少．
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">45 + 6</gadget>
<output>51</output>

<result>51</result>