A football ticket is 15 yuan. After the price reduction, the audience doubles and the income increases (1/5). How much is the price of a ticket reduced?
足球门票一张15元，减价后观众增加一倍，收入增加了(1/5)，一张门票降价多少元．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(6/5) / 2</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">15 * (3/5)</gadget>
<output>9</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<result>6</result>