There is such a thing as "Adhesive Remover" sold in carpet installation stores. I have never seen it at Big Box stores. It dissolves the glue but it is still gooey but you then scoop it up with a putty knife. Slow work for sure. Having not seen the floor in question I cannot speculate as to how long it will take you or how much you should charge, but here is my formula for figuring that our. Take your expected hourly rate i.e. $50 per hour, and multiply that by how many hours you think it will take you and add it the cost of materials i.e. $80 and you have your answer.