Chapter 4.5, Problem 60ES

A concrete barrier whose cross section is an isosceles triangle runs parallel to a wall. The height of the barrier is $3\text{ ft,}$ the width of the base of a cross section is $8\text{ ft,}$ and the barrier is positioned on level ground with its base $1\text{ ft}$ from the wall. A straight, stiff metal rod of negligible diameter has one end on the ground, the other end against the wall, and touches the top of the barrier (Figure Ex-60). What is the minimum length the rod can have?