week time series value forecast forecast error absolute value of forecast error squared forecast error percentage error absolute value of percentage error 1 18 2 13 18 -5 5 25 -38.46 38.46 3 16 13 3 3 9 18.75 18.75 4 11 16 -5 5 25 -45.45 45.45 5 15 11 6 6 36 35.29 35.29 6 14 15 -1 1 1 -7.14 7.14 totals 20 96 -37.01 145.09 a. mae? b. mse? c. mape? d. the forecast error for week 7?