I really don't understand what you are asking your words are not making sense
Answer:
(x + 39) or x = -39
Step-by-step explanation:
Set f(x) to 0
0 = 5x + 195
5x = -195
x = -39
24 x ^2 + 54 x + 21,
if you would like me to explain how to do it, I can in the comments.
= 
and then solve for x.