Uncle Zhang did a small renovation for a certain company this month, and received a one-time labor fee of 4,000 yuan from the company. If the balance exceeds 800 yuan, he will pay personal income tax at a rate of 20%. How much tax should Uncle Zhang pay?
张叔叔这个月给某公司搞了一个小型装修，一次性从公司领到劳务费4000元，如果超过800元后的余额，按照20%的税率缴纳个人所得税．张叔叔应该缴纳税款多少元？
<gadget id="calculator">4_000 - 800</gadget>
<output>3_200</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3_200 * (1/5)</gadget>
<output>640</output>

<result>640</result>