Question 791437
The rectangle is split into two right triangles if you add in a diagonal. So use the pythagorean theorem.


a^2 + b^2 = c^2


5^2 + b^2 = 13^2


25 + b^2 = 169


b^2 = 169 - 25


b^2 = 144


b = sqrt(144) ... note: b is never negative


b = 12


So the length is 12 meters.