Question 894923
A garment manufacturer's total revenue function is given by the equation R(y)=-3y^2+522y-320 where "y" is the number of units. Find the marginal revenue, /MR, for garments at y=21

This is the only thing left in my chapter that is confusing me.  Can someone please help.  Thank you.
<pre>
To calculate marginal revenue, find the derivative of the revenue function, and then substitute number of units
into the derivative function.
Therefore, {{{R(y)= - 3y^2 + 522y - 320}}} becomes: {{{MR(y) = - 6y + 522}}}, which becomes: {{{MR(y) = - 6(21) + 522}}} ----- Substituting 21 for y
{{{MR(y) = - 126 + 522}}}, or {{{highlight_green(MR(y) = 396)}}}.
You can do the check!! 

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