[tex]AC=10[/tex]
1) The first thing we need to do is to find x, using the Perimeter, i.e. the sum of the sides:
[tex]\begin{gathered} x+1+2x+x+3=40 \\ \\ 4x+4=40 \\ \\ 4x+4-4=40-4 \\ \\ 4x=36 \\ \\ \frac{4x}{4}=\frac{36}{4} \\ \\ x=9 \end{gathered}[/tex]
2) Note that the question is what is the length of AC. So we can plug x=9 into the AC expression:
[tex]\begin{gathered} AC=x+1 \\ \\ AC=9+1 \\ \\ AC=10 \end{gathered}[/tex]
