To find the value of b we solve the first equation for a, then we have:
[tex]a=13-3b[/tex]now we plug this value into the second equation:
[tex]\begin{gathered} (13-3b)+b=5 \\ 13-2b=5 \\ 13-5=2b \\ 2b=8 \\ b=\frac{8}{2} \\ b=4 \end{gathered}[/tex]Therefore b=4
