Answer:
11.87m/s
Explanation:
To solve this problem it is necessary to apply the concepts related to frictional force and centripetal force.
The frictional force of an object is given by the equation

Where,
Friction Coefficient
N = Normal Force, given also as mass for acceleration gravity
In the other hand we have that centripetal force is given by,

The force experienced to stay on the road through friction is equal to that of the centripetal force, therefore


Re-arrange to find the velocity,



Therefore the speed that it is necessaty to slow down the car in order to make the curve without sliding is 11.87m/s