Answer:
Part a)
E = 4812.5 N/C
Part b)
Two field must be perpendicular to each other as well as perpendicular to the velocity of charge so that net force on the moving charge will be zero
Step-by-step explanation:
For uniform electric and magnetic field we will have a charge particle moving through it such that net force on it is zero
so here we have

magnetic force on moving charge will balanced by electrostatic force on moving charge

now we have

B = 0.550 T
now we have


Part b)
Two field must be perpendicular to each other as well as perpendicular to the velocity of charge so that net force on the moving charge will be zero