2015 SQA Advanced Higher Mathematics No.18 First order differential equation model

Work through an extended problem using first order differential equations. Instructional exercise consisting of question 18 from the 2015 SQA Advanced Higher Mathematics examination. Where appropriate the alternative methods for solving the problem are also given. Set out in stages of 'try then check' the worked solution to each part of the question. Including indications of where each mark is allocated, and the requirements for that mark, according to the marking scheme.