For the Second part, I think answer should be as follows:
f = (V^2/ 15R) - 0.01 e
where,
f = Side friction, which depends on road type, condition and speed of vehicle
V = Speed in mph, R = Radius in ft
e = Road super elevation
Since f depends on speed as well, the solution should be in quadratic form.
Suppose, e =0 (no superelevation)

Speed (mph)             f-value
10                             0.21
20                             0.21
30                             0.18
40                             0.16
50                             0.14
60                             0.13
70 & more                 take 0.10

So, pick a f value, calculate speed and check if it matches for your speed taken for that f-value.
(I forgot equation for f -value)

For Example:
e =0, f=0.17, R = 558 ft (170m)
Hence, V= 37 mph, and for this speed f=0.17
I guess, your answer should be 37 mph.