If two firecrackers produce a combined sound level of 85 db when fired simultaneously at a certain place, what will be the sound level if only one is exploded?

82dB

Explanation: The decibel is a logarithmic unit expressed as the ratio of 2 signal values such as power, pressure, intensity etc.

truck y has a greater velocity than truck x.

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 =