Sales of Volkswagen's popular Beetle have grown steadily at auto dealerships in Nevada during the past $5$ years $($see tablebelow$).$ Sales of Volkswagen's popular Beetle have grown steadily at auto dealerships in Nevada during the past $5$ years $($see table below$).$ Year Sales $12345051051857045585$ a$)$ Forecasted sales for year $6$ using the trend projection $($linear regression$)$ method are $625\mathrm{.}6$ sales $($round your response to one decimal place$).$ b$)$ The MAD for a linear regression forecast is $10\mathrm{.}72$ sales $($round your response to one decimal place$).$ c$)$ The MSE for the linear regression forecast is sales $($round your response to one decimal place$).$