Sales over the past $10$ years are shown below. Using the method of least squares, calculate the values of a and b to complete this regression equation. Year Sales

$11,590$

$21,270$

$31,760$

$41,430$

$51,980$

$61,300$

$71,140$

$81,460$

$91,570$

$101,130$ Sales? and forecast for next year's sales