We know that the incenter is equidistant from the side, this imply that
[tex]\begin{gathered} AI=BI=C= \\ 3x+7=5x-11=52-2x \end{gathered}[/tex]From the 1st and 2nd equation, we get
[tex]\begin{gathered} 3x+7=5x-11 \\ 7+11=5x-3x \\ 18=2x \\ \text{then} \\ x=\frac{18}{2} \\ x=9 \end{gathered}[/tex]Now, we can substitute this values into AI and get
[tex]\begin{gathered} AI=3x+7 \\ AI=3(9)+7 \\ AI=34 \end{gathered}[/tex]then, the answer is AI= 34 units