It is 21 meters more than 500 meters (4/5), how many meters is it?
比500米的(4/5)还多21米，是多少米．
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">500 * (4/5)</gadget>
<output>400</output>

<gadget id="calculator">400 + 21</gadget>
<output>421</output>

<result>421</result>