Example 3: For a batch of cement, 45 vehicles are needed to load it with a small truck; only 36 vehicles are needed to load it with a large truck. Each large truck is loaded with 4 tons more than the small truck. How many tons is this batch of cement?
例3：一批水泥，用小车装载，要用45辆；用大车装载，只要36辆．每辆大车比小车多装4吨，这批水泥有多少吨？
<gadget id="calculator">1 / 36</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">1 / 45</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">(1/36) - (1/45)</gadget>
<output>1/180 = around 0.005556</output>

<gadget id="calculator">4 / (1/180)</gadget>
<output>720</output>

<result>720</result>