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Find the relative rate of change of f(x) at the indicated value of x. 20. f(x) = 72; x =230 21. f(x) = 404 -4x; x = 38 Find the percentage rate of change of f(x) at the indicated value of x. 22. f(x) = 476 + 161x; x =2 23. f(x) = 18,000 - 4x2; x = 65 Use the price-demand equation to determine whether demand is elastic, inelastic, or has unit elasticity at the indicated value of p. P4. x = f(p) = 7,290 - 30p , p = 10 25. x = f(p) = 10,980 - 7p - 0.4p , p=90, p = 100, p = 85 reasing at the 26. A fast food restaurant can 155 Ifthe daily sales at