Question

Please tell me if I am right or way off. Given a quantity demanded function of q = - p2 + 29 p + 10 where q represents copies of a book sold per week and p ranges from (20 < p < 30 ). Determine the price of the book that will generate the maximum revenue.

R=P*Q
R=p(-p^2+29p+10)
R(p)=-p^3+29p^2+10p
p (10+29p+-1p^2)=0
a=-1 b=29 c=10
(-29+/-(square root)29^2-4(-1)(10))/-2 p=-.340 or p=29.34 or p=0

I was also considering doing it like this.
R=P*Q
R=p(-p^2+29p+10)
R(p)=-p^3+29p^2+10p
DerivativeR(p)= -3p^2+58p+10
0= -3p^2+58p+10
X=-.1709 or x=19.5