The longest side of a triangle is always opposite the largest angle of a triangle.
If the smallest angle of the triangle is 20 degrees, then the shortest side is opposite to it. Using this information, we can form the equality
20/100(longest leg/biggest angle) = x/20(shortest leg/smallest angle)
We can cross multiply this to get 400 = 100x. From here it is a simple "find x" and the shortest side is 4 feet.
