First, you substitute x with 10 (recall that when -8x means -8 times x)
[tex] \frac{ - 8(10) + 9}{ - 9 + 10} [/tex]
For the numerator (the top), you use PEMDAS (first multiply -8 and 10, then add 9):
[tex] \frac{ - 80 + 9}{ 1} [/tex]
When the denominator (the bottom) is 1, you can just write the numerator:
-80 + 9
That equals - 71