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A manufacture has been selling 1400 television sets a week at $450 each. A market survey indicates that for each $20 rebate offered to a buyer, the number of sets sold will increase by 200 per week. a) Find the demand function p(), where a is the number of the television sets sold per week. p(I) b) How large rebate should the company offer to a buyer, in order to maximize its revenue? c) If the weekly cost function is 105000 + 150x, how should it set the size of the rebate to maximize its profit