The only thing i fail to understand is your calculation of the downhill slope. How exactly do you arrive at the 1/2.16 number with the slope of down 6in and a distance of 13ft?
6/13 = 1/2.16.
So I clarified that in my post, thanks to you :-)
"....You must determine the fraction that the slope (6 inches) and the stated distance (13 feet) together represent: 6/13 = 1/2.16. You then multiply 43.43 by this fraction (43.43 X 1/2.16 = 43.43/2.16), and add the product of this multiplication (20.11) to 43.43, which gives 63.54...."