The two brothers took a total of 200 yuan to the bookstore to buy reference books. After returning home, the two brothers had exactly the same amount of money left. It is known that the ratio of the amount of money spent by the elder brother to his original amount is 3:7, and the ratio of the amount of money spent by the younger brother to his original amount is 9:13. How much did my brother spend?
兄弟两人共带200元钱去书店买参考书，回家后两人剩下的钱数正好相等．已知哥哥花去的钱数与他原来钱数的比是3：7，弟弟花去的钱数与他原来钱数的比是9：13．哥哥花去多少元钱？
<gadget id="calculator">7 + 13</gadget>
<output>20</output>

<gadget id="calculator">200 / 20</gadget>
<output>10</output>

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

<result>30</result>