problem:

lim as x -> 4 : 4-x / (5 - sqrt(x^2 + 9))

I tried to use the conjugate property but in the end when I substitute 4 into the equation I come up with it turns to:

(4 - 4) * (5 + sqrt(4^2 + 9)) / 25 - 16 + 9

0 * 5 + 5 / 18

the answer should be 5/4, where am I going wrong with this problem?