Functions and Quotient

Question

Let f(x) be the function 1 / x+5. Then the quotient f(5+ℎ)-f(5) / h can be simplified to -1 / aℎ+b for:

a=

and

b= 

(I've been able to get a, which is 10 but for some reason I keep getting b as 0 and that's not correct.)

Answer 1

f(x)=1/(x+5)

f(5)=1/10

f(5+h)=1/(10+h)

f(5+h)-f(5)=-h/(100+10h)

[f(x+5)-f(5)]/h=-1/(100+10h)

b=100