please solve this problem using these formulas

Question 6: Week 12 Question 2, (7 Marks) Amex PLC has gathered following information on the sales of face mask from April 2020 to September 2020. Month Sales ($) April 17,000 May 18,000 June 19,500 July 22,000 August 21,000 September 23,000 You are required to a. Using linear trend equation forecast the sales of face masks for October 2020. (5 marks) b. Calculate the forecasted sales difference if you use 3-period weighted moving average designed with the following weights: July 0.2, August 0.3 and September 0.5. (2 marks) Time Series Regression b, r=[(t - 7)(y - y)] X=(t- bo = Y - bei Te = bot but