"A small block, with a mass of 250 g, starts from rest at the top of a ramp. It then slides without friction down the incline, around the loop at the bottom and then onto the final level section.
The maximum height of the incline is 80 cm, and the radius of the loop is 15 cm."

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 =