ok you can turn them from fractions into an equation where they are in the form (ax) not (a/x)
to do this find the reciprocal of the value being divided as timesing the reciprocal is the same as dividing by the value before.
Sorry im struggling to put it into words but hopefully if i go through the examples it will make mores sence.
x/45= to x times by 1/45 . to differentiate you minus the power of x which is 1 in this case and times it by the value of 1/45. so 1x 1/45 = 1/45
3/x^4= 3x^-4 as the reciprocal of x^4 = x^-4. once again to differentiate minus the power of x by 1 so x is now x^-5 and times the number in front by the previous value of the power which was -4. so the answer would be -12x^-5
3x^2/5 is simpler as it is already in the form (ax). as the power is 2/5 we minus that by 1 so we get -3/5 as the new power and times 3 by the previous power of 2/5. so the answer to this would be 1.2x^-3/5.
I hope i made this easy to understand if not just say and ill try to explain it better.