This problem is examining HSC Physics Module 5 Advanced Mechanics. Even though the object is a charged particle, it will still behave like a projectile subjected to a uniform force and a uniform acceleration.
Instead of a gravitational field, the alpha particle is subjected to an electric field.
You should draw the diagram referred to in Part (a). Draw the direction of the uniform force vector that the alpha particle will experience.
Part (b) Using the equation for the force F = Q.E you should calculate the magnitude of the force. So you have these data: the mass of the particle, the initial velocity of the particle, and a uniform acceleration a = Q.E/m.
Do you think you can finish the problem now?