The historical demand for a product is: Week 1 2 3 4 5 Demand 40 70 100 130 160 Forecast the demand in the 6 th week by (a) using a 4-week simple moving average (1 point). (b) using a 4-week weighted moving average with weights of 0.4, 0.3, 0.2, and 0.1 (2 points). (c) using an exponential smoothing with a = 0.8 and the 4th week forecast =120 (2 steps and 2 points). (d) finding the trend line y = a + bx, and using it to forecast (5 points).