this is my 2nd question in over 12+ hours.

$\displaystyle \left[\begin{matrix}x+y&x+z\\y+z&w\end{matrix}\\]$

Equals

$\displaystyle \left[\begin{matrix}3&4\\5&4\end{matrix}\\]$

i got

x + y = 3 x+z = 5

y + z = 5 w=4

and i don't know what to do from there. text book is really horrible.