What is the acceleration of a proton moving with a speed of 6.5 m/s at right angles to a magnetic field of 1.8 t ?

The magnetic force acting on the proton is 

where
q is the proton charge
v is its speed
B is the intensity of the magnetic field
is the angle between the direction of v and B; since the proton is moving perpendicular to the magnetic field,  and , so the force becomes


this force provides the centripetal force that keeps the proton in circular motion:

where the term on the left is the centripetal force, with
m being the mass of the proton
r the radius of its orbit

Re-arranging the previous equation, we can find the radius of the proton's orbit:


And now we can calculate the centripetal acceleration of the proton, which is given by

Ibelieve the correct answer would be c.