Find AC please, help is very much appreciated.

Answer:
AC ≈ 67.9
Step-by-step explanation:
15² = 9 (3x + 1 + 9)
225 = 9 (3x + 10)
225 = 27x + 90
135 = 27x
x ≈ 19.29
AC = (3x + 1 + 9)
AC = 3 (19.2857...) + 1 + 9
AC = 57.857... + 1 + 9
AC = 57.857... + 10
AC ≈ 67.9