Suppose Y denotes the matrix of shape (N,1) which contains N ground-truth values in a linear regression problem. The matrix X is of shape (N,D) with each column denoting an independent feature for the same problem. Let N>D. The optimal solution for this setting, when calculated analytically, is given by? (Note: A^{-1} denotes the inverse of A whenever it exists and A' denotes the transpose of A when A is a matrix) *