The angle of elevation of a ladder leaning against a wall is 60º and the foot of the ladder is 12.4 m away from the wall. The length of the ladder is:

Answer: Option D

Consider the diagram shown above where PR represents the ladder and RQ represents the wall.
$$\begin{array}{rl}& \cos 60^{\circ }=\frac{PQ}{PR}\\ & \frac{1}{2}=\frac{12.4}{PR}\\ & PR=2\times 12.4\\ & =24.8m\end{array}$$