Section $9$:

The figure below shows the graph of the revenue function $R(x)($in dollars$)$ for selling $x$ hats. What is the average rate of change in revenue from selling $20$ hats to selling $40$ hats? Draw the secant line.

revenue

Consider the cost function $C(x)=12000+8000x$ for producing $x$ widescreen TVs where $x$ is measured in $100\text{'}$s of TVs$.$

a$.$ Find the change in cost when production changes from $2000$ to $3000$ TVs$.$

b$.$ Find the average rate of change of cost for this change in production levels.