Chapter R - Elementary Algebra Review - R.2 Equations, Inequalities, and Problem Solving - R.2 Exercise Set - Page 946: 25

$x=-15$

Removing the grouping symbols and combining like terms, the value of the variable that satisfies the given expression, $ 4-(6+x)=13 ,$ is \begin{array}{l}\require{cancel} 4-6-x=13 \\\\ -x=13-4+6 \\\\ -x=15 \\\\ x=-15 .\end{array}