The ratio of the number of volleyballs to the number of footballs in the school sports room is 9:10, and the number of footballs is less than that of basketballs (2/7). There are 69 known basketballs and volleyballs, how many footballs are there?
学校体育室里排球个数与足球个数的比是9：10，足球的个数比篮球少(2/7)．已知篮球与排球共有69个，足球有多少个？
<gadget id="calculator">9 + 14</gadget>
<output>23</output>

<gadget id="calculator">69 / 23</gadget>
<output>3</output>

<gadget id="calculator">3 * 10</gadget>
<output>30</output>

<result>30</result>