If you were doing this not for coursework I'd personally use the inbuilt sorting function of whatever language you are using as this would almost certainly be the most efficient, however to score better on the complexity it'd be a good place to implement your own sorting algorithm. Looking at the mark scheme, a merge sort would probably look the most impressive as recursive algorithms are generally thought of as more complex.
Have you covered recursive algorithms yet in the theory section of your lessons? If so you can probably easily adapt the algorithm from one of the exam questions or the teaching resources. Or you can just look up examples that other people have created. (Although the examples in the text book to me seem needlessly complex, and I prefer a method where two functions are used one for division and one for merging)