Percent Yield help~~~~?

Question

How do I do this problem?

43. The percent yield of the following reaction is consistently 92%.

CH4(g) + 4S(g) ---> CS2(g) + 2H2S(g)

How many grams of sulfur would be needed to obtain 80.0 g of CS2?

Also ---

45. Tin (IV) chloride is produced in 81.1% yield by the reaction of tin with chlorine. How much tin is required to produce a kilogram of tin(IV) chloride?

Answer 1

Moles CS2 = 80.0 g / 76.143 g/mol =1.05

Moles S = 4 x 1.05 =4.20

Mass S = 4.20 x 32.066 g/mol =134.8 g ( theoretical mass)

Mass S = 134.8 x 100 / 92 = 146.5 g needed

Sn + 2 Cl2 >> SnCl4

Moles SnCl4 = 1000 g /260.5 g/mol=3.84

Moles Sn = 3.84

Mass Sn = 3.84 mol x 118.710 g/mol = 455.8 g ( theoretical mass)

455.8 x 100 / 81.1 = 562.1 g needed