Determine the molar m of the unknown solid. Is the unknown solid NaCO3,NaHCO3,NA3PO4, or KHC8H4O4?

I think you have mis-asked the question. I think that the boiling point of the unknown solute solution in water is 89.0C. This is a 11degC boiling point depression. From the boiling point depression, you have to work back to the molaltity of the unknown solute in the solution. The m of solute in water is 4.41g. The m of water is 99.72g. Molaltity is moles of solute in 1 kg (1000g) solvent (water). I think that Kb is degreesC/molal.