This question appears to contain some information that can be misinterpreted because of language differences.  The following assumptions are being made concerning the information provided:
Tank diameter = 3 meters
Tank height = 3 meters
Shaft diameter = 0.1 meters
Density of milk of lime: rho = 1042 kg/m^3
Impeller diameter: D = 1.4 meters
Rotational speed = 40 rpm, N = 0.667 revolutions/second [rps]
Number of blades on the impeller = 6
Blade angle = 60/10 from horizontal or arctan(6) = 80 degrees from horizontal
Estimated power number Np = 4.7

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