good running time needed

5. (14%) Let A[1..n] be an array of n positive numbers. Entry Ali] represents the trading price of a stock X on the i-th day (and hence the numbers are ordered chronologically). Write an algorithm max-profit that returns a pair (a, b) such that if one buys stock X on the a-th day and sells it on the b-th day, the maximum profit is made. Give the time complexity of your algorithm in Big-O. Show the derivation of the complexity result