How many liters of methane gas (ch4) need to be combusted to produce 12.4 liters of water vapor, if all measurements are taken at the same temperature and pressure? show all of the work used to solve this problem.
ch4 (g) + 2o2 (g) yields co2 (g) + 2h2o (g)

Since litres is the subject of the question, molar mass will be considered in litres. 
Since the question didn't specify if it was a complete combustion or incomplete combustion, we assume that it is a complete combustion. 
Mr(CH4) =16
Mr (O2)= 32 
Mr(H20)=18 
so, 16 litres of methane will produce 36 litres of water vapour. How many litres of methane will combust to produce 12.4 litres of H20? 
Cross multiply. 
(12.4 x 16) / 36 = 5.51 litres. 

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic