In triangle XYZ, points L, M and N are the midpoints of sides XY, XZ and YZ respectively.
a. (i) Prove that quadrilateral YLMN is a parallelogram.
b. (ii) Show that the area of quadrilateral YLMN is exactly half the area of triangle XYZ.
c. (iii) If XY=8cm, XZ=10cm and YZ=12cm, find the perimeter of quadrilateral YLMN."