If a tree of 5.5 meters casts a shadow of 3 meters. How high will a tower that gives a shadow of 15 meters be?

The height of a tower would be 27.5 meters

Explanation:

Notice that in both cases you are dealing with diagrams representing vertical objects and shadows created by the sun, against the ground, so we are in the presence of right angle triangles which have in common another angle (that made by the rays of the sun. So we can use similar triangles and the proportion that is generated based on the quotient of similar sides to find the unknown height (h).

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 =