What is the mass, in kilograms, of an avogadro's number of people, if the average mass of a person is 150 lb ?

First step is to convert the lb to kg as follows:
1 lb = 0.45 kg
Therefore, 150 lb = 150 x 0.45 = 67.5 kg

Avogadro's number = 6.02 x 10^23

Mass of Avogadro's number of people = 6.02 x 10^23 x 67.5  
                                                              = 4.0635 x 10^25 kg

Fitness is the ability to perform only very light levels of physical activity.