Vector Algebra

If x, y and z are non-zero real numbers and \(a = x\widehat i + 2\widehat j,b = y\widehat j + 3\widehat k\) and \(c = x\widehat i + y\widehat j + z\widehat k\) are such that \(a \times b = z\widehat i - 3\widehat j + \widehat k\), then [a b c] is equal to