Answer:

Step-by-step explanation:
In order to add or subtract numbers in scientific notation, the powers of ten must have the same exponent. In this caes the diameter of an average human body cell is a power of -4 and the diameter of a plant cell is a power of -3. In order to add them, we can move the decimal over for the body cell diameter:

Add the two values: 
That would first be a conversion factor is a number used to change one set of units to another, by multiplying or dividing. when a conversion is necessasry
Hello,
tan 60°=√3
d/39=tan 60°==>d=39/√3=39√3/3=13√3=22,516660498... (m)