Five years ago, the age of the mother was four times that of the daughter. The mother is 45 years old this year. How old is the daughter?
5年前妈妈的年龄是女儿的4倍，妈妈今年45岁，女儿今年几岁了？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">45 - 5</gadget>
<output>40</output>

<gadget id="calculator">20 + 40</gadget>
<output>60</output>

<gadget id="calculator">60 / 4</gadget>
<output>15</output>

<result>15</result>