I have a 2" square stock 1/4 thick hollow. It's 210" long. It's being supported on each end by 4". How much weight can it hold in the center

It's 1018 cold steel 1/4" rounded edges and hollow. I just need approximately how much weight it can hold in the middle. It is supported on both sides by 4". Total piece is 210". Just need an idea of weight it can hold not using this to live underneath it, it was just holding something up in the backyard shed just need an idea that soul can't hold 200 pounds 100 pounds Etc. It's also floating on cinder blocks 4 inches on each side