Okay! So, first, you need to draw perpendicular lines from the radii to the triangle like this:
https://ibb.co/FJ6m67v (picture is not mine)
Since the triangle is a triangle, and the lines are perpendicular, you have created a 30-60-90 triangle. Using the 30-60-90 side lengths, we can get AG = 2root{3}. Same thing with HC, as they are symetrical.
DGHF is a rectangle, which means GH = 2+2 = 4
So AC = 4root(3) + 4. => I got 4root(3) from multiplying 2root(3) by 2 (there are two per side), and 4 from the value we got before .
Multiply that by 3, and you get 12root(3)+12 for your answer!
(Please correct me if I am wrong. I'm not the best at geometry! )