(a) Since the equation is:

And "L" is in meters, the cos per meter will be simply the slope of the line. Alternatively, we can just input L = 1 and check the corresponding cost:

So, the cost is $0.80 per meter.
(b) Now, we have to the the contrary, we input 1 input "p" and calculate "L":

So, it will be 1.25 meters long.