Answer:
C.
Explanation:
as M is right over the middle of LN, this is an isoceles triangle (both legs are equally long).
so, we need to calculate only one leg and then double it fit both legs.
we get e.g. LM via Pythagoras.
LM is the Hypotenuse of the right-angled triangle with half of LN and the height to M being the legs.
so,
LM² = height² + (LN/2)² = 3² + 6² = 9 + 36 = 45
LM = sqrt(45) = 6.708203932... units
the perimeter is the sum of all 3 sides :
LN + LM + MN = LN + 2×LM = 12 + 2×sqrt(45) =
= 25.41640786... units