Light with a wavelength of 654 nm passes through two slits that are separated by 0.0225 mm and makes an interference pattern on a screen. The distance from the
center bright spot to the first bright band is 19.5 mm. Find the distance in base SI
units from the slits to the screen behind them.

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 =

t = 1/400 h   ⇔ 0.0025 h ⇔ 9s ⇔ 0.15 m

any of the answers are correct.

the doppler effect is used by weather forecasters to measure 

moving clouds