Acar with a mass of 1200 kilograms is moving around a circular curve at a uniform velocity of 20 m/s the centripetal force on the car is 6000 neutrons what is the radius of the curve

Coupla things wrong with this question, Sam.
Let's clean those up first, and then we'll work on the answer.

-- The car is NOT moving with uniform velocity.
'Velocity' includes both speed and direction.  If either of these
changes, it's a change of velocity.
On a circular track, the car's direction is CONSTANTLY changing,
so its velocity is too. 
The thing that's uniform is its speed, not its velocity.

-- A 'neutron' is a subatomic particle found in the nucleus of most
atoms.  It's not a unit of force.  The unit of force is the 'Newton'.


OK. A centripetal force of 6,000 newtons keeps 1,200 kg of mass
moving in a circle at 20 m/s.

The formula:

                                     Centripetal force = (mass) (speed)² / (radius)

Multiply each side
by 'radius':                (centripetal force) x (radius) = (mass) x (speed)²

Divide each side by
'centripetal force':       Radius = (mass) x (speed)² / (centripetal force)

Write in the numbers
that we know:              Radius = (1200 kg) (20 m/s)² / (6000 Newtons)

                                                 = (1200 kg) (400 m²/s²) / (6000 Newtons)

                                                 = (480,000 kg-m²/s²) / (6000 kg-m/s²)

                                                 = (480,000 / 6000) meters
                                                
                                                 =         80 meters .   

She sold 135 peaches, because if you multiply 2.50 eith 135, you'd get 337.5, the 0 can be added or not.