Chemistry questions, please help?

1. The compound styrene, a hydrocarbon used in the production of Styrofoam, is comprised of two elements: hydrogen and carbon. Elemental analysis reveals that a 50.00 g sample of pure styrene contains 46.13 g of carbon. How many moles of hydrogen atoms are in this sample?

2. An aqueous solution containing excess magnesium chloride is mixed with the saturated solution of lithium phosphate (Ksp = 2.37 x 10-4) in 200.0 mL of water until excess solid is present.
How many grams of the new solid precipitates?
Net ionic equation for the reaction that results:
3Mg2+(aq) + 2PO43-(aq) -> Mg3(PO4)2(s)