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.
