Methane and CO2 atmospheric lifetime math problem

[courtneywetts]

Homework Statement

On a per-molecule basis, methane is 26 times more effective as an infrared absorber than is CO2. Calculate the corresponding ratio on a per-unit-mass basis, and compare it with the 20-year GWP for methane. What's the reason for any discrepncy you find?
(CO2 atmospheric lifetime = 1000 years, GWP relative to CO2 is 1 in 20 years)
(Methane atmospheric lifetime = 11 years, global warming potential relative to CO2 in 20 years is 23)

Homework Equations

The Attempt at a Solution

I am not sure how to start this problem. I think I need to make a ratio between methane and CO2 but am not sure if that is right or how to do so.

 

[Hollumber]

It gives you the ratio between their effectiveness per molecule. How to change this ratio considering the effectiveness per mass instead of molecule?

 

[haruspex]

Suppose 1 molecule of CO2 has absorption rating X.
Complete the following:
1 molecule of methane has absorption rating ...
1 molecule of methane has mass ... atomic units
1 molecule of CO2 has mass ... atomic units
... atomic units of CO2 has absorption rating X
1 atomic unit of CO2 has absorption rating ...
1 atomic unit of methane has absorption rating ...