we have two equation and two variables:
[tex]\begin{gathered} y=3x+4 \\ y=-2x-1 \end{gathered}[/tex]Now we can substitude the first equation into the second equation:
[tex]3x+4=-2x-1[/tex]Now we move all the terms with an x to the left and the constants to the right
[tex]3x+2x=-1-4[/tex]and we simplify
[tex]\begin{gathered} 5x=-5 \\ x=-\frac{5}{5} \\ x=-1 \end{gathered}[/tex]Now with the value of x, we can substitude into any equation, I am going to use the first one:
[tex]\begin{gathered} y=3x+4 \\ y=3(-1)+4 \\ y=-3+4 \\ y=1 \end{gathered}[/tex]