Both F's are forces, so µ must be unitless/dimensionless.
F[friction] = µ F[normal]
Or, more explicitly in terms of the units:
(Newtons) = (constant) (Newtons)
b) from the burning of fossil fuels
c) from hydroelectric power plants and dams
d) as a waste product from nuclear power plants
Answer: They are added into they air by burning fossil fuels
Explanation: When fossil fuels burn, they add Carbon dioxide into the atmosphere
Hope This helped- God Bless