This answer is in response to multiple questions, the primary of which follow the answer.  The answers to the basic questions are easier than the explanation for the calculations.
 
Question:
1. Type of impeller? PBT - 4-blade, pitched (45 degree) blade turbines.
2. Number of impeller? 2 impellers, one 150 mm off-bottom and the other 300 mm off-bottom.
3. Impeller dimension?  Both impellers 275 mm in diameter with 55 mm wide blades
4. Rotational speed? 350 rpm
5. Shaft dimension? Diameter 38 mm by 1040 mm long
6. Power required? Minimum motor power 3.75 KW
7. Material of construction for impeller and its shaft? Carbon Steel
8. Please guide me how I can calculate them. (if possible) Suggested References:  Handbook of Industrial Mixing (John Wiley, 2004);   The High-Efficiency Road to Liquid-Solid Agitation Chemical Engineering (October 1994, pp. 138-144); How the Design of Shafts, Seals and Impellers Affects Agitator Performance (Chemical Engineering , August 30, 1976, pp. 101-108).

The answers by this expert are based on the best available interpretation of the information provided.  The consequences of the application of this information are the responsibility of the user.  If clarification is needed, please submit a further question.