The expression x-7 divided by 9-x^2 is undefined when x

If this helps at all, the problem can equal out to 0 if x=7, hope this helps. :)

You have x-7/ 9-x^2. 
An expression is undefined when the denominator = 0.
What value is x to make 9-x^2 = 0?
Maybe 3?
3^2 = 9
9-9 =0

Hope this helps! 

The slope best fit isc. 1/6 mile per hour