How many sections are there in the provided content?
Based on the given context, there are 6 sections. The sections are indicated by the use of "by" followed by a numerical value (e.g., s. 36). These indicate separate sections within the provided content:

1. Section number not mentioned in the context
2. Section 28 (w.e.f. 20-6-1979)
3. Section number not mentioned in the context
4. Section 28 (w.e.f. 20-6-1979)
5. Section 36 (w.e.f. 3-1-1977)
6. Section 4(b) (with retrospective effect)

Therefore, there are a total of 6 sections in the provided content.