A student has current income y1 and expects future income y2. She plans current consumption c1 and future consumption c2 in order to maximise utility U = 2∑c1 + 2̢∑c2, c1, c2 > 0 where ̢ > 0 is her discount factor. If she borrows now, c1 > y1, then future consumption, after repaying the loan c1 - y1 with interest r, will be c2 = y2 - (1+r)(c1 - y1). Alternatively, if she saves now, c1 < y1, future consumption will be c2 = y2 + (1+r)(y1 - c1) after receiving interest r on her savings. The student takes the interest rate r as given. Answer the following questions: (a) [5 marks] State carefully the maximisation decision of the student. (b) [8 marks] Find the optimal plan (c1*, c2*). Show your workings and interpret your results. (c) [7 marks] Show how an increase in the interest rate affects the level of borrowing or saving. Show your workings.