Its all about Magnetic Flux density

Show your solution, thank you!

31.19 A certain solenoid (50 cm long with 2000 loops) carries a current of 0.70 A and is in vacuum. An electron is shot at an angle of 10 to the solenoid axis from a point on the axis. (a) What must be the speed of the electron if it is to just miss hitting the inside of the 1.6 cm diameter solenoid? (b) What is then the pitch of the electron's helical path? Ans. (a) 1.4 x 10' m/s; (b) 14 cm