Draw a diagram of the situation:
Notice that a right triangle is formed with the ramp, the horizontal side and the vertical side.
Use the Pythagorean Theorem to find the length L:
[tex]\begin{gathered} L=\sqrt[]{(12)^2+(5)^2} \\ =\sqrt[]{144+25} \\ =\sqrt[]{169} \\ =13 \end{gathered}[/tex]
Therefore, the length of the ramp is 13 feet.
