Hello topher0805When the car is travelling at 60 km/h (v = 50/3 m/sec), assuming there is no tendency to slide:

R(horiz) , where is normal contact force with road and = radius of bend

R(vert)

Eliminate :

(1)

When speed = 90 km/h (v = 25 m/sec) and car is on point of sliding:

R(horiz) (2)

R(vert)

(3)

Eliminate from (2) and (3):

, from (1)

Now solve for and you're done.

Grandad