Question 1133343
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I hope you don't really mean what you say.  Profit is the difference between what you make (revenue) and what your costs are (cost).  So profit = revenue minus cost.<br>
You are given the revenue and cost functions; build the profit function P(x) by subtracting the cost function from the revenue function.  (Watch your signs when doing the subtraction!)<br>
For the second part, the average rate of change in the profit from year 3 to year 5 is the difference in profit between year 3 and year 5 (P(5)-P(3)), divided by the number of years from year 3 to year 5 (5-3=2).