15 yuan per pot of flowers, buy 3 pots and get 1 pot free, buy 3 pots at once, how much is each pot cheaper?
每盆花15元，买3盆送1盆，一次性买3盆，每盆便宜多少元？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 * (3/4)</gadget>
<output>45/4 = around 11.25</output>

<gadget id="calculator">15 - (45/4)</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>