The amount if prawn caught per week on a trawler is a function of the crew size

The amount if prawn caught per week on a trawler is a function of the crew size assigned to operate the boat. Based on past data, the following production schedule was developed:

Crew Size Amount of prawn caught per week
(Number of worker) (Hundreds of LBS)
2 3
3 6
4 11
5 19
6 24
7 28
8 31
9 33
10 34
11 34
12 33

a.) Over what ranges of workers are there (i) increasing, (ii) constant, (iii) decreasing and (iv) negative returns?
b.) How large a crew should be used if the trawler owner is interested in maximizing the total amount of prawn caught?