Calculating energy difference between two 1-4 dimethylcyclohexane conformers

The following question was asked in a quiz at my college



> 
> Draw the most stable and least stable chair conformer for 1,4-dimethylcyclohexane and calculate the
> energy difference between these two. Given that the value for CH3-H diaxial interaction = 3.8 kJ/mol and
> CH3-CH3 gauche interaction = 3.8 kJ/mol. Ignore the gauche interaction with the ring C atoms
> 
> 
> 


I drew the Newman projection but I am unable to understand how to proceed further as to which CH3-H pairs to consider and which not to, also in the Newman projection will the two methyl even interact?


