Please help if you can!!

the gateway arch was designed by eero saarinen and was constructed using the equation
y=211.49-20.6cosh(0.03291765x)
for the central curve of the arch, where x and y are in meters and the absolute value of x is less than or equal to 91.20

if the height is 60 m at the points (-81, 60) and (81, 60), what is the slope of the arch at these points?



Answer :