describes the friction.
In my opinion the friction has to be greater than the centrifugal force (otherwise you'll leave the lane and land in the ditch).
2. If I'm right you only have to plug in the given values into the inequatlity
and solve for v.
3. You'll get the speed in m/s. Convert it into km/h and compare with the allowed speed. You'll see, that the limitation is not sufficient.