There are 30 red and white balls in a bag, and A, B, and C each take 10 of them. It is known that the number of red balls held by A is twice the number of white balls held by B, and the number of red balls held by B is twice the number of white balls held by C. If the total number of white balls is an odd number, how many red balls are there?
袋里有30个红球和白球，甲、乙、丙各拿了其中的10个．已知甲拿的红球数是乙的白球的2倍，乙的红球数是丙的白球数的2倍，白球的总数是奇数，则红球有多少个．
<gadget id="calculator">8 + 6 + 7</gadget>
<output>21</output>

<result>21</result>