i guess a good way to flesh it out would be to firstly go through exactly what a marketing plan is, and why it is important for the plan to be efficient... you could put a couple of case studies in here - one that had a good marketing plan and one that had a bad one... then say how understanding the target market improves the efficiency of the plan i.e. the target market determines your place, product, price and promotion strategies... then you could go show that when each of the 4 Ps are efficient, the marketing plan is efficient...
i think the key part is that the target market determines the details of the marketing plan...
also, extended responses for business studies dont have to be in essay form...you hav to do sect 3 in report format, and you can if u want do sect 4 in report format as well..