Use the substitution method to solve the system of equations:
[tex]\begin{gathered} x+y=18 \\ x=4+y \end{gathered}[/tex]Since x is already isolated on the second equation, replace x with the expression for x in the first equation:
[tex]\begin{gathered} x+y=18 \\ \Rightarrow(4+y)+y=18 \\ \Rightarrow4+2y=18 \\ \Rightarrow2y=18-4 \\ \Rightarrow2y=14 \\ \Rightarrow y=\frac{14}{2} \\ \therefore y=7 \end{gathered}[/tex]Substitute y=7 into the expression for x:
[tex]\begin{gathered} x=4+y \\ \Rightarrow x=4+7 \\ \therefore x=11 \end{gathered}[/tex]Therefore, the solution for this system of equations, is:
[tex]\begin{gathered} x=11 \\ y=7 \end{gathered}[/tex]