This topic is the topic of the sixth grade of primary school. The questioner came out without thinking. The word "deduction" in the title will cause disagreement, that is, the "deducted" 800 yuan belongs to the country, should it be handed in, or should the 800 yuan belong to itself (that is, Teacher Shi). Although people who know a little about taxation know that this "deducted 800" should actually be understood as "beyond 800 yuan", that is to say, this 800 yuan is ultimately owned by Teacher Shi, so 2640/( 1-20%) = 3300 yuan.

3300+800=4 100 yuan

A: The fee for this manuscript is 4 100 yuan.

By the way, in primary schools, there are ambiguous problems in the tutoring assignments of each grade. Teachers in different schools have different answers. When correcting, the teacher will only judge right or wrong according to his own understanding, confusing the students, and the students in both schools will argue endlessly. Publishers only care about making money, who cares about quality? )