Help???

First off, i really havent been paying attention in my class, so i really am not doing too hot in there. I have 4 questions that i need help on. or if you give me the equations i will solve them myself.
What mass of H2SO4 would be required to prepare 750mL of a 0.15M H2SO4 solution?
Determine the freezing point of a solution made by adding 27.5 g of Na2SO3 to 250.0 g of water.
If a saturated solution fo AgNO3 at 20C contains 216 g AgNO3 per 100.0 g of water, what mass of water could contain 725 g of this solute at the same temperature?
A 0.350 sample of a large molecular compound was dissolved in 15.0g of chloroform. The freezing point depression of this solution was determined to be 0.240C. Calculate the molar mass of the molecular solute. The Kf for chloroform is 4.07C/m

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