(20 points) Let A[1::n] be an array of distinct positive integers, and let t be a positive integer. (a) (10 points) Assuming that A is sorted, show that in O(n) time it can be decided if A contains two distinct elements x and y such that x + y = t. (b) (10 points) Use part (a) to show that the following problem, re- ferred to as the 3-Sum problem, can be solved in O(n2) time: 3-Sum Given an array A[1::n] of distinct positive integers, and a positive integer t, determine whether or not there are three distinct elements x, y, z in A such that x+y+z = t.