It is of common that most of us write the units of quantities in a wrong format or commit similar mistake.
All the symbols of quantities we write should start with a small letter not with a capital letter.
For ex. while writing unit for time: 3 hrs is the correct but not 3Hrs which a blunder mistake we all might have committed one or the other time.
The above rule is applicable in all cases except when the symbol is named after a person. In this case if it is a single lettered symbol it should be written in capitals and otherwise the first letter should be capital and all other letters in lower case.
For ex. The unit for force which is Newton should be written as 400N but not as 400n
Ex. Also the unit of pressure Pascal named after great scientist Pascal should be written as 400Pa but not 400pa or 400PA.
It should be also noted that while using prefixes like kilo etc these should be written in small cases while the unit in upper case.
For ex. while writing 100kilo Newtons we should write it as 100kN.