Xiaoying is 3 years younger than Xiaoming. The sum of their ages this year is half the age of the teacher. In 15 years, the sum of their ages will be equal to the age of the teacher. How old is Xiaoying this year?
小英比小明小3岁，今年他们的年龄和是老师年龄的一半，再过15年，他们的年龄和就等于老师的年龄，今年小英是多少岁．
<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<result>6</result>