Chapter 3 - Equations and Problem Solving - 3.3 - More on Solving Equations and Problem Solving - Problem Set 3.3 - Page 114: 15

$x=-3$

Using the properties of equality and combining like terms, the value of the variable that satisfies the given equation, $ 6x+1=3x-8 ,$ is \begin{array}{l}\require{cancel} 6x-3x=-8-1 \\\\ 3x=-9 \\\\ x=\dfrac{-9}{3} \\\\ x=-3 .\end{array}