Three years ago, the elder brother was twice as old as the younger brother. Three years later, the combined age of the two brothers is 30. How old is the elder brother?
3年前，哥哥的年龄是弟弟的2倍，3年后，哥弟俩的年龄和是30岁，哥哥今年多少岁？
<gadget id="calculator">30 - 3 - 3 - 3 - 3</gadget>
<output>18</output>

<gadget id="calculator">1 + 2</gadget>
<output>3</output>

<gadget id="calculator">18 / 3</gadget>
<output>6</output>

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

<gadget id="calculator">12 + 3</gadget>
<output>15</output>

<result>15</result>