两平面\(\alpha{,}\beta\)的法向量分别为\(\overrightarrow{u}{=}(3{,}{-}1{,}z){,}\overrightarrow{v}{=}({-}2{,}{-}y{,}1)\)，若\(\alpha{⊥}\beta\)，则\(y{+}z\)的值是\(({  })\)