Question

The new vapor pressure of a solution of 3.25g of an unknown compound in 22.35g of H2O is 114.9mmHg at 55 degrees Celcius. What is the molar mass of the unknown compound?
Note the correct spelling of celsius.

Psoln = XH2O*Pnormal
Substitute for Psoln 114.9, look up vapor pressure of H2O at 55 C and substitute for Pnormal, solve for XH2O.

Then
moles H2O/(moles H2O+moles unknown) = XH2O from above.
Substitute moles H2O (from grams/molar mass) and solve for moles unknown.

You know moles = grams/molar mass. You know grams and moles, solve for molar mass.

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