These Charlie Harper Serigraphs are probably worth about $200-400 respectively if they are unframed in their original sleeves.

Unfortunately framing practices varied tremendously in the 1970's and if these are not really framed to conservation standards, then their value is diminished. Examine the bevels of the matting and if these are yellowish brown...that's a sign that they were not handled properly.

Selling through Ebay is your best bet, or to a gallery that handles Harper's work.

Regards