7.
平面向量\( \overrightarrow{a}\),\( \overrightarrow{b}\),\( \overrightarrow{c}\),\( \overrightarrow{a}=(-1,1)\),\( \overrightarrow{b}=(2,3)\),\( \overrightarrow{c}=(-2,k)\),若\( \overrightarrow{a}+ \overrightarrow{b}\)与\( \overrightarrow{c}\)平行,则实数\(k=\) ______ .