I need help with a math problem
Mathematics

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Sally found when she charged $75 the
number of video tapings demanded per year was 80. At a video taping price of $100, the demand
dropped to 60. Given that this is
linear, find the demand equation. Above
what price will there be no demand? What is the maximum quantity demanded?
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To derive the demand equation, we must understand that price is on the y axis while quantity is on the x axis.
Therefore, the slope of the demand curve is given by (75100)/(8060) = 1.25
The equation is Y=1.25x + c
where Y  quantity demanded, xprice and c is a constant
takong one point say (80,75) we have 75 = 1.25(80)+c ;c= 175
Therefore demand equation is Y = 1751.25X
The price above which there will be no demand is the price when quantity demanded is zero or the Yintercept.
Hence, Y=1751.25(0) =175
When price goes beyond 175, demand is zero.
The maximum quantity demanded is the quantity demanded when price is zero or the Xintercept.
Hence 0=1751.25X; 1.25X=175
X=175/1.25 = 140
Maximum demand is 140
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