Please fill in natural numbers in □ and ○ in the equation 2009*□+4*○=6099 to make the equation valid. What is the sum of the numbers filled in the two □?
请在等式2009*□+4*○=6099的□与○填入自然数，使等式成立，问两个□中所填的数字之和是多少？
<gadget id="calculator">3 + 18</gadget>
<output>21</output>

<result>21</result>