The equation of the line can be shown using the slope intercept form that is
y= mx+b
where m is the slope and b is the y intercept
So firstly we have to find the value of slope m
To find the value of slope m we apply the formula

So we can plug the values using the two given points
(-0.5,0.75) and (0.75,-0.5)

So m = -1
Plug m=-1 in the equation we get
y= -1x +b
Now we have to find the value of b
to find the value of b , we plug any one pint in the equation
0.75 = -1(-0.5) +b
0.75 = 0.5 +b
Subtract 0.5 from both sides
0.25 = b
or
b= 0.25
Now plug the value of b , in the equation
we get
y = -1x +0.25
hence the equation of the line is y = -1x +0.25
Given that,
Total cost function, C (x) = 43x + $1850
The revenue function R (x) = $80x
To find,
The number of units that must be produced and sold to break even.
Solution,
At break even, cost = revenue
43x + $1850 = $80x
Subtract 80x from both sides.
43x + 1850 -80x = $80x -80x
1850 = 80x-43x
37x = 1850
x = 50
So, the required number of units are 50.
Total amount paid if he bought = 6000 + 726(12 x 3) = 6000 + 726(36) = 6000 + 26,136 = 32,136
Total amount paid if he rents = 2000 + 37P, where P is the monthly rent
For renting to be cheaper
2000 + 37P < 32,136
37P < 32136 - 2000 = 30136
P < 30136 / 37 = 814.49
Therefore, the maximum rent he could pay is $814
Rearranging the first equation gives:

Substituting this into the other equation gives:

If x=-1:

So
x=-1, y=-5
I am assuming you mean 3.0 *10^8 and 1.5 * 10^11.
time = distance/speed right. So,
t = 500 s