It could be one of many “space frame” bikes built by Murray of Ohio for any one of many distributors. Sears, JC Pennys, Gambles, OTASCO, K-Mart, Wards, etc. Murray used the same frame then changed racks, chain guards, tanks, etc. for each distributo. The numbers stamped into the left dropout can be decoded using the Murray serial number project thread on this site. Easiest way to find it is to Google the thread by name.