open vs closed vs hyphenated - Hyphenation for "300 or 400 level"

Since "400 level" should be hyphenated as "400-level", should "300 or 400 level" be hyphenated as "300- or 400-level," or is there another way to write this?

Answer

"300- or 400-level" is correct. However, if you have "to" in between, I would write it as "300-to-400 level" or "300-to-400-level".