Inscribed angles. so i answered 54, but that's wrong and it says the correct answer is 84, i wanna know how to answer it so i can do corrections

The most important rule you need to understand for this question is that two tangents that meet at an external point are equal. That is, the tangent AJ meet at an external point to BJ (hence, they are equal by this rule).

In doing this, AJ = BJ, BK = CK, and CL = AL
We know the dimensions for each side now.

So, your perimeter becomes: 2(13 + 14 + 15) = 84 units.