Question 302036
4/z plus 7/z-5

you need to obtain common denominator before adding the numerator.

the denominator = z(z-5) 
but remember to multiply the same factor to the numerator too i.e

4/z = [4*(z-5)]/[z*(z-5)]
7/z-5 = [7*z /(z*(z-5))]

So the sum becomes:

[4*(z-5) + 7*z] / [z(z-5)]

[4z - 20 + 7z] / [z(z-5)]

(11z-20)/z(z-5) (hence shown)