Past Trial Maxima and Minima Problem (1 Viewer)

[Thomasta3]

http://gyazo.com/456457ba9a74711f3c3e1e1aadc9a9bc

Above is a question from my school's 2013 trial paper. Maxima and minima would have to be my worst topic, and I can't figure out this question. The question is only worth 3 marks, so I assume it's not THAT difficult, but nonetheless I am hopeless with this. Can anyone please work it out and put it in a way that even a toddler could understand? Thanks in advance.

 

[Thomasta3]

I've solved it, for i) at least. Wouldn't hurt for someone to check my ii) answer. Sorry, I can't write it in fancy mathematical format on the forums (as I for one cannot be bothered) so I will post my working via photos:
i) http://gyazo.com/36e10e48736ff955880940eff4573456
ii) http://gyazo.com/0e6f4656b1835261ee714534bd4e5318

Sorry that they're on the side...