Acar with a mass of 1200 kilograms is moving around a circular curve at a uniform velocity of 20 meters per second. the centripetal force on the car is 6000 newtons. what is the radius of the curve?

Well, first of all, a car moving around a circular curve is not moving
with uniform velocity.  The direction of motion is part of velocity, and
the direction is constantly changing on a curve.

The centripetal force that keeps an object moving in a circle is

         Force  =  (mass of the object) · (speed)² / (radius of the circle)

         F  =  m s² / r

We want to know the radius, to rearrange the formula to give us
the radius as a function of everything else.

                                          F     =  m s² / r

Multiply each side by 'r':       F· r  =  m · s²

Divide each side by 'F':            r  =  m · s² / F    

We know all the numbers on the right side,
so we can pluggum in:

                      r  =       m       ·        s²      /     F

                      r  =  (1200 kg) · (20 m/s)² / (6000 N) .

I'm pretty sure you can finish it up from here.