text: I'll help you with the first part, but unfortunately you were ambiguous with your terminology.  Is R = P(x) [P is a function of x] or R = P*x, i.e., P(x)*x, i.e., the function P times x?  Not only that, you say R = px, lower case p, which strictly means p is another variable you have not mentioned yet.  While that's what you wrote, I doubt that's what you meant.\n\nI'm going to assume you meant R = P(x) - if not, use the same logic by multiplying through by x.\n\nP(x) = sqr(x) - 10x + 25\nR(max) = P'(x) for x = 0 (derivative of P(x) = 0 implies the maximum)\n\nSo take the derivative of P(x) and set P'(x) = 0.  Find x.  Replace this value for x in the original equation and you will have R(max).\n\n2 and 3:  Again, here you literally imply there is a new variable, p.  If that's what you mean there isn't enough info to help.  If you really mean P(x) = 2 and 3, then do the following:\n\nSolve for x in P(x) = 2 and 3\n\nReplace this variable in your Marginal revenue, which you've defined as R' = P'(x) which you found in (1) (or you'll have to recalculate if I misinterpreted your Revenue function).\n\nDo the same in the elasticity function, which you have not written down.