$-$ The president of a small manufacturing firm is concerned about the continual growth in manufacturing costs in the past several years. The data series of the cost per unit for the firm$$s leading product over the past $8$ years is as follows:

$$a$.$ Construct a chart for this time series. Does a linear trend appear to exist?

$$b$.$ Develop a simple linear regression model for these data. What average cost increase has the firm been realizing per year?