Low energy conformations determining

PROBLEM 4.37 Draw three-dimensional pictures of all the stereoisomers of 3,4-dimethylheptane and 3,5-dimethylheptane. It is probably easiest to draw them in the ecUpsed arrangement, even though this is not a low-energy conformation. Determine the absolute configuration R or S) of each stereogenic carbon. Designate the stereogenic carbons with an asterisk. 

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