to get the equation of any straight line, we simply need two points off of it, let's use those two points in the picture below.

keeping in mind that for the point-slope form, either point will do, in this case we used the second one, but the first one would have worked just the same.
Answer:
$2.10x + 5= $49.10
x=21
Step-by-step explanation:
the x is used for a variable that changes and in this case the mph changes which lead x being the amount of miles that they had drove which at the end ends up multi. with the $2.10 . as for the 5 it was an initial as in it doesn't change.
for the second part
you subtract 5 from each side so you have the total of 2.10x= 44.10 then u divide 2.10 from each side and that will give you x = 21
Answer:
AC = 30
Step-by-step explanation:
Start with:

Combine like terms.

Subtract
from both sides of the equation.

Subtract
from both sides of the equation.

Then, substitute
for
in 

Multiply.

Finally, add.

Answer:
(The image is not provided, so i draw an idea of how i supposed that the problem is, the image is at the bottom)
Ok, we have a rectangle of length x by r.
At the extremes of length r, we add two semicircles.
So the perimeter will be equal to:
Two times x, plus the perimeter of the two semicircles (that can be thought as only one circle).
The radius of the semicircles is r, and the perimeter of a circle is:
C = 2*pi*r
where pi = 3.14
Then the perimeter of the track is:
P = 2*x + 2*pi*r.
b) now we want to solve this for x, this means isolating x in one side of the equation.
P - 2*pi*r = 2*x
P/2 - pi*r = x.
c) now we have:
P = 660ft
r = 50ft
then we can replace the values and find x.
x = 660ft/2 - 3.14*50ft = 173ft