Answer:
(5) The perpendicular height of the triangle is 8.48 mm.
(6) The 1184.86 cm far up the wall the ladder reach.
Explanation:
Part (5):
When a perpendicular is drawn in an isosceles triangle then the perpendicular divided the base into 2 equal parts.
The figures is shown below.
In ΔABC,
CB = 6 mm
So,
CD = BD = 3 mm
Now calculating the perpendicular height of the triangle.
Using Pythagoras theorem in ΔADC:

Thus, the perpendicular height of the triangle is 8.48 mm.
Part (6):
The figure is shown below.
Converting meter to centimeter:
1 m = 100 cm
So,
12 m = 1200 cm
Using Pythagoras theorem in ΔXYZ:

Thus, 1184.86 cm far up the wall the ladder reach.