A manufacturer has been selling 1100 television sets a week at $420 each. A market survey indicates that for each $21 rebate offered to a buyer, the number of sets sold will increase by 210 per week. a) Find the demand function p(a), where x is the number of the television sets sold per week. p(ac) = b) How large rebate should the company offer to a buyer, in order to maximize its revenue? c) If the weekly cost function is 77000 + 140x, how should it set the size of the rebate to maximize its profit