A high-speed test track for cars has a curved

section — an arc of a circle of radius R =
1440 m. The curved section is banked at
angle a = 19.1 degrees from the horizontal to help
the cars to stay in the road while moving at
high speeds.
The acceleration of gravity is 9.8 m/s^2 .

One day, oil spills on the track making a
few meters of the curved section frictionless.
Calculate the speed v of a car which can cross
the oil spill of the curve without slipping sideways.
Correct answer: 69.9051 m/s.

I'm supposed to figure out how they got this answer in order to apply this concept to a similar problem but I'm unsure as of how to do it.