Answer:

Step-by-step explanation:
The domain of a rational function is all real numbers <em>except </em>for when the denominator equals 0.
So, to find the domain restrictions, set the denominator to 0 and solve for x.
We have the rational function:

Set the denominator to 0:

Subtract 9:

So, the domain is all real numbers except for -9.
In other words, our domain is all values to the left of negative 9 and to the right of negative 9.
In interval notation, this is:

And we're done :)
Answer:
You forgot to post your mistake.
Step-by-step explanation:
If y=8-x then you can plug that into the equation like 7=2-(8-x). When you distribute the equation becomes 7=2-8+x. Once you combine like terms the equation becomes 7=-6+x. Then you subtract 6 from both sides, which gives you 13=x.
To find y just put 13 where x was in the first equation. Y=8-13.
Y=-5
X=13
<span>So he bikes 21 miles in 4.2 hours, which is 5 mph. </span>