A 58.72 kg person holding a steel ball stands motionless on a frozen lake. The person then throws the ball, which propels the person at 1.05 m/s to the
right and the ball 3.75 m/s to the left. If the initial momentum of the system is
zero, what is the mass of the steel ball?

16.44 kg

Explanation:

Apex ;)

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =