Math Help - Check my work

1. Check my work

Items are sold for $45 each. 195 people are willing to buy them. For every$5 increase in price, 5 fewer people are willing to buy the item. Determine the maximum revenue and the number of price increases.

Let x be the number of increments.
Let y be the total cost.

$y=(195-5x)(45+5x)$
$y=-25x^2+750x+8775$
$y=-25(x^2-30x+225) (-225)(-25)+(8775)$
$y=-25(x-15)^2+14400$

Where total revenue = \$14400
Where total numer of increases = 15

2. Very good!
Specially if the -225(-25) were written not too close to the -25(x^2 -30x +225).
As posted, the two terms appeared multiplied to each other.