Let \(A=\{x_1, x_2, \ldots, x_7\}\) and \(B=\{y_1, y_2, y_3\}\) be two sets containing seven and three distinct elements respectively. Then the total number of functions \(f: A \to B\) that are onto, if there exist exactly three elements \(x\) in \(A\) such that \(f(x)=y_2\), is equal to :