Length of Xianren Bridge is 400 feet.
l represents the length of other natural arches.
Since, Xianren Bridge is the longest arch, we have,
l < 400
Let's graph this inequality.
Take the other natural arches along x-axis and the lengths along y-axis.
Clearly, the graph of l = 400 is a straight line parallel to x-axis.
So, l < 400 is the region below the line l = 400.
