first solve the parenthesis
[tex]4x-40=-3x-12[/tex]then, place the x's on the same side and the other numbers on the other side
[tex]\begin{gathered} 4x+3x=-12+40 \\ \end{gathered}[/tex]do the operations
[tex]7x=28[/tex]solve x
[tex]\begin{gathered} x=\frac{28}{7} \\ \\ x=4 \end{gathered}[/tex]the value of x is 4
you can check the solution replacing x on the initial expression
[tex]4((4)-10)=-3(4)-12[/tex]and solve each side
[tex]\begin{gathered} 4(-6)=-12-12 \\ -24=-24 \end{gathered}[/tex]the equality is right