A toothpaste outlet diameter is 5mm, each squeeze 1cm of toothpaste, can be used 40 times, how many milliliters of this toothpaste.
一支牙膏出口直径为5mm，每次挤1cm的牙膏，可以使用40次，这支牙膏有多少毫升．
<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">3.14 * (25/4) * 1 * 10 * 40</gadget>
<output>7_850</output>

<result>7_850</result>