Doudou's father is an editor. Once he published an article, he paid 420 yuan's contribution fee and asked for his total contribution fee.

According to the national regulations, the calculation method of tax payment for personal articles and books is as follows: (1) No tax is paid if it is not higher than 800 yuan; (2) If the contribution fee is not higher than 4,000 yuan in 800 yuan, the part exceeding 800 yuan shall be taxed at 14% of the contribution fee; (3) If the manuscript fee is more than 4,000 yuan, the tax of 1 1% shall be paid.

Assuming that Doudou Dad is between 800 and 4000, then (x-800)× 14%=420 gives x=3800.

And 3800 is just between 800 and 4000, so Mr. Chen's manuscript fee should be 3800 yuan.