Answer:
(a). The magnitude of the magnetic field is 
(b). The time required for the electron to move from A to B is
.
(c). The magnetic field is 0.2943 T.
Explanation:
Given that,
Speed 
We need to calculate the magnetic field
Using formula of magnetic force and centripetal force



Where, m = mass of electron
v = speed of electron
q = charge of electron
r = radius of circular path
Put the value into the formula



The direction of the magnetic field must be into the page by the right hand and curls finger rule.
(b). The time required for the electron to move from A to B will be given as :
We need to calculate the time
Using formula of time

Where, d = total distance traveled by an electron
v = speed of electron
Put the value into the formula


The time required for the electron to move from A to B is
.
(c). If the particle were a proton instead of an electron
We need to calculate the magnetic field
Using formula of magnetic field

Put the value into the formula


The magnetic field is 0.2943 T.
Hence, (a). The magnitude of the magnetic field is 
(b). The time required for the electron to move from A to B is
.
(c). The magnetic field is 0.2943 T.