Answer:
4.5 cm
Step-by-step explanation:
KL = LM as triangle is isosceles
LM = KM as LF = FM = KN = NM, so the triangle is equilateral
EF ║ NM as LE⊥EF and LN⊥NM
EF is half the midsegment as ∠KLN ≅ ∠MLN, and LN is angle bisector of ∠KLM
Midsegment is half the side length, and all sides are 18 cm.
EF = 1/2(1/2*18) = 4.5 cm
