how many grams of a protein weighing 4500 grams/ mol must be present in 100 ml of water solution to a given osmotic pressure of 18 mm hg at 25 degrees celcius...( use formula of pie = Mrt

That's pi, not pie; and celsius is spelled celsius. :-).

pi = MRT
Solve for M = molarity.
M = moles/L. You have L and M, solve for moles.

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