There was originally 8L of water in the water tank, then 420mL was added, and another 3500mL was drawn out. How much water is there in the water tank now?
水缸里原来有水8L，后加入420mL，又抽出3500mL，现在水缸里有多少水？
<gadget id="calculator">8 * 1_000</gadget>
<output>8_000</output>

<gadget id="calculator">420 - 3_500</gadget>
<output>-3_080</output>

<gadget id="calculator">8_000 + (-3_080)</gadget>
<output>4_920</output>

<result>4_920</result>