MHB Vertical / Horizontal Displacements

[JJKD]

Hey guys! Firstly, let me start by apologizing if this is completely the wrong place to put this question. As you'll soon tell my maths is... well, questionable at best.

Let me just give some context to avoid any assumptions :) I'm starting an OU degree in autumn with my first module being mathematics. My maths knowledge didn't get any further than high school so it's a bit of a challenge. I've been trying to revise using practise papers and bring myself at least up to scratch but this is proving difficult. There are some questions where I'm spending hours on them which would take some of you 10 minutes. But this question here is driving me nuts...

The question:

A boy standing on a level playing field kicks a ball into the air from the
ground at his feet. The trajectory of the ball can be modeled by the
equation

y=3x - x^2/2

where x is the horizontal displacement (in metres) of the ball from the
boy and y is the vertical displacement (in metres) measured from the
ground.

(i) Find the maximum vertical displacement of the ball.

(ii) If there is a 3 metre high wall at a distance of 5 metres from the
boy, in the direction the ball is travelling, will the ball be kicked
over the wall? Explain your answer.​

I have lots more questions like this but I want to work those out myself when I have an understanding of the first one :/

Sorry this is a pretty big 'text dump', but my math ability is pretty bad and I don't even know where to begin.

Cheers guys!
Jay

 

[Greg]

(i) What does the $y$-coordinate of the vertex of the parabola represent?

(ii) What is the value of $y$ when $x$ is 5?