The son's age this year is the father's (1/6), and the son's age after 4 years is the father's (1/4). How old is father?
儿子今年的年龄是父亲的(1/6)，4年后儿子的年龄是父亲的(1/4)．父亲今年多少岁？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">6 - 1</gadget>
<output>5</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/3) - (1/5)</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">4 / (2/15)</gadget>
<output>30</output>

<gadget id="calculator">6 / 5</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">30 * (6/5)</gadget>
<output>36</output>

<result>36</result>