M1 help!

Hola, basically I'm doing M1 and I kind of hate maths at the moment so bare with me if I ask any ridiculous really obvious questions.

I've got an old exam question from 2003 & our teacher gave us all the final answer for it but I'm confused as to how she got it.

5. A particle P moved with constant acceleration (2i-3j)m/s^-2. At time t seconds, it's velocity is v/m/s^-1. When t=0, v=-2i+7j.

a. Find the value of t when P is moving parallel to the vector i. (I've done this bit & got it correct. The answer is t= 2 and a third seconds.)

b. Find the speed of P when t=3. (this is the bit I'm ridiculously stuck on. I don't understand how to get to the answer, is there a formula or something I should know about that and I'm just being a bit dense?)

c. Find the angle between the vector j and the direction of motion of P when t=3. (Haven't yet tried this, but I suck at maths so all help would be appreciated.)

Thank you for your help in advance, even if you have to roll your eyes at my stupidity please help me

Part b is just SUVAT because you have constant acceleration. But remember that the velocity is a vector, so to find the speed you need the magnitude of velocity.