the demand function given was q= -p(squared) + 33p +9 (18<- p <- 28) copies sold per week where price is p dollars. the question was determine what price the company should charge to obtain largest revenue. they also gave a cost function of c= 9p+100.. they wanted to know largest weekly profit also.

I tryed to do the rev pq and do derivatives but i kept coming up with squaring a negative..

Could someone help me out i'd greatly appreciate it!!