The table below shows the incomes and rates of income tax levied on four professionals in an economy.
 

Profession	Income per month($)	Tax rate %	Disposable income ($)
Doctor	8,000	10
Engineer	7,000	12
Civil servant	5,000	18
Nurse	6,000	15

Use the above data to answer the questions that follows: 

(a) Calculate the disposable incomes of the four individuals

(b) What system of taxtation was employed?

(c) Give reasons for your answer in 2(b)

(d) With the aid of a diagram, explain the system of taxation employed in 2(b)