The age of the elder sister is three times the age of the younger sister at that time. The age of the older sister is the same as the age of the younger sister. The sum of the ages of the elder sister and the younger sister is 25 years old. How old is the elder sister now?
姐姐现在的年龄是妹妹当年年龄的三倍，姐姐当年的年龄与妹妹现在的年龄相同，姐姐和妹妹现在的年龄之和是25岁，姐姐现在是多少岁？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">25 / 5</gadget>
<output>5</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>