Xiaodong is a student in the fourth grade of elementary school. The sum of the ages of him and his father is 48 years old. Three years ago, what was the sum of their ages?
小东是小学四年级的学生，他和爸爸今年年龄的和是48岁，三年前，两人年龄的和是多少岁．
<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">48 - 6</gadget>
<output>42</output>

<result>42</result>