Question

A)What mass of carbon dioxide is produced from the complete combustion of 7.00×10−3 g of methane?

B)What mass of oxygen is needed for the complete combustion of 7.00×10−3 g of methane?

Answer 1

Here is a link that will work all of your stoichiometry problems. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html

Answer 2

Write the balanced equation.

CH4+2O2 >> CO2 + 2H20

for each mole of carbon dioxide produced, one mole of methane, and two moles of oxygen is used.

Moles methane: .007/(16.04)

Answer 3

.0385g