Verified Answer :

well, we now that the original fraction is 90/600

In order to simplify the fraction, we just need to divide both numerator and denominator with a same number until it couldn't be divided anymore. Let's try to divide them with 30

which makes  3/20

hope this helps

to find 90 as a fraction of 600
divide 90 by 600
we have 90/600
divide both numerator and denominator by 30
3/20
so 90 is 3/20 th of 600