1. The standard form of of −399/603?

Dear Aakarsh,
Here is your answer:
(-399) ÷ 3  = (-133)
  603 ÷ 3         201

To find any more common factor of (-133) and (201), we have to find common factors between their absolute values, i.e. 133 and 201. 
See, to find more common factors we need to see any common factor of (+133) and 201
Factors of 133 = 1,7,19,133
Factors of 201 = 1,3,67,201

So, you can see that there is no more single common factor between 133 and 201 other than 1. 

That is why we can't simplify (-133)/201 further..


Thus,
Standard form of (-399/603) is (-133)/201.

Hope it helps!

Regards!