Answer
15,000 discs, 3.75
Work Step by Step
Demand: $p=-.01x^2 - .2x+9$
Supply: $p=.01x^2-.01x+3$
$-.01x^2-.2x+9=.01x^2-.1x+3$
$-.01x^2-.2x+9+.01x^2+.2x-9=.01x^2-.1x+3+.01x^2+.2x-9$
$0 = .02x^2+.1x-6$
$0*50 =(.02x^2+.1x-6)*100$
$0 = x^2+5x-300$
$(x-15)(x+20)=0$
$x-15=0$
$x-15+15=0+15$
$x=15$
$x+20=0$
$x+20-20=0-20$
$x=-20$
We can’t have a negative quantity, so $x=15$.
$p=.01x^2-.01x+3$
$x=15$
$p=.01x^2-.1x+3$
$p=.01*15^2-.1*15+3$
$p=.01*225-1.5+3$
$p=2.25+1.5$
$p=3.75$
