Column calculation: the sum of (3/4) and (2/5) is multiplied by their difference, what is the product?
列式计算：(3/4)与(2/5)的和乘以它们的差，积是多少？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/4) + (2/5)</gadget>
<output>23/20 = around 1.15</output>

<gadget id="calculator">(3/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(23/20) * (7/20)</gadget>
<output>161/400 = around 0.4025</output>

<result>161/400 = around 0.4025</result>