<PRE><B>Question 255988</B>
if you right, they you want to find f(-b/2a)


take the value of 7 and plug it into the equation to get:


y=-10x^2+140x+18000 becomes:


y=-10(7)^2+140(7)+18000 becomes:


y = -490 + 980 + 18000 = 18490 which should be the maximum rent he collects for the month.


graph of your equation looks like:


{{{graph (600,600,-10,75,-5000,25000,-10*x^2 + 140*x + 18000)}}}


y looks like it represents the total rent for the month.


x looks like it represents the number of units vacant for the month.


based on that the graph looks good.


7 vacant rooms means 43 filled at 360 + 70 = 430 per room = 18490.
6 vacant rooms means 44 filled at 360 + 60 = 420 per room = 18480.
8 vacant rooms means 42 filled at 360 + 80 = 440 per room = 18480.


you definitely get peak revenue with 7 vacant rooms.







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