The age of the elder brother 5 years ago is equal to the age of the younger sister 7 years later, the sum of the ages of the elder brother 3 years later and the age of the younger sister 7 years ago is 30 years old, how old is the younger sister this year?
哥哥5年前的年龄等于妹妹7年后的年龄，哥哥3年后与妹妹7年前的年龄和是30岁，妹妹今年多少岁？
<gadget id="calculator">30 - 5 - 7 - 3</gadget>
<output>15</output>

<gadget id="calculator">7 + 15</gadget>
<output>22</output>

<gadget id="calculator">1 + 1</gadget>
<output>2</output>

<gadget id="calculator">22 / 2</gadget>
<output>11</output>

<result>11</result>