Here's a way without matrixes:
Adding all 4 equations gives us \(3(w+x+y+z) = 33\), meaning \(w+ x + y + z = 11\).
Using this, we know \(w = -1\), \(x = -8\), \(y = 7\), and \(z = 13\).
So, we have \((-1 \times -8) + (7 \times 13) = \color{brown}\boxed{99}\)
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