1. Taxation is a common form of obtaining fiscal revenue. Compared with other forms of fiscal revenue, it has the formal characteristics of compulsory, free and fixed, and is customarily called "three natures".

2. The free fluctuation of price is the basic premise of tax burden transfer, and the elasticity of commodity supply and demand, market structure, cost change and tax system are the constraints and influencing factors.

3. Taxation is the main source of fiscal revenue; It is an important means to regulate economic operation; It is an important tool to adjust income distribution; Having the function of supervising economic activities; In foreign exchanges, taxation also plays an important role in safeguarding national rights and interests.

Calculation problem:

(1) payroll tax = (5800-3500) *10%-105 =125.

(2) Individual tax on remuneration = (4000-800) * 20% * (1-30%) = 448.

(3) Assessment fee (labor remuneration) individual tax =( 1000-800)*20%=40.

(4) Individual tax on sun's remuneration = (18000-3000) * (1-20%) * 20% * (1-30%) =1680.

Note: Sun's donation =18000/30000 * 5000 = 0.6 * 5000 = 3000.

The personal tax rate table given in the title is the latest tax rate table, deducting 3500 yuan.