Question 774618
This is a Pythagorean question involving
the solving of the length of the hypotenuse
represented by the ladder.
The vertical side of the triangle is the
wall and measures 12m.
The base side of the triangle is the 
distance the foot of the ladder is away from
the wall.
Vertical side^2 + Base side^2 = Hypotenuse^2
12^2 + 5^2 + Hypotenuse^2
Hypotenuse = {{{sqrt(12^2 + 5^2)}}}
Hypotenuse = {{{sqrt(169)}}}
Hyoptenuse = 13
Therefore the length of the ladder
= 13 metres.
Hope this helps.
:-)