Question 747206
this is a Pythagorean question
Imagine a right angled triangle with
the house wall being the vertical side 
and the ground being the bottom horizontal
side.
The length of the ladder is given by 
the value of the hypotenuse, the side
facing the right angle.
The square on the hypotenuse = the sum
of the squares on the other two sides.
12^2 + 5^2 = 169
Square root of 169 = 13ft.
The length of the ladder required
is 13ft.