Seven years ago, the age of the older sister was four times that of the younger sister; seven years later, the sum of the ages of the two sisters was 48 years old, how old is the elder sister?
7年前，姐姐的年龄是妹妹的4倍；7年后姐妹俩的年龄和是48岁，姐姐今年多少岁．
<gadget id="calculator">7 + 7</gadget>
<output>14</output>

<gadget id="calculator">48 - 14 - 14</gadget>
<output>20</output>

<gadget id="calculator">20 + 7</gadget>
<output>27</output>

<result>27</result>