$($a$)$ Use the two $($year$,$ sales$)$ data points $(1,70)$ and $(3,146)$ to find the linear relationship $y=mxb$ between $x=$ years since $2010$ and $y=$ sales $($in millions$).$

$($b$)$ Interpret the slope of the line.

Sales are increasing by $38$ million unit's per year.

Sales are increasing by $32$ million units per year.

Sales are decreasing by $32$ million units per year.

Sales are decreasing by $38$ million units per year.

Sales cycle between at $70$ million