4. An arch bridge with a span of 120 m long is composed of two intersecting parabolic arch. The p...

4. An arch bridge with a span of 120 m long is composed of two intersecting parabolic arch. The peak of the higher arch is 30 m high; while, the peak of the lower arch is 18 m high. The arches are secured with vertical "stringers" are 8 m apart starting from the supports, What is the sum of the lengths of the stringer used in the bridge?