Replacement of both rear gas strut assemblies

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I was told that my rear gas strut is leaking fluid and recommends to replace pair of rear gas strut assemblies (1.2 hrs labor per side) and a 4 wheel alignment for $668 plus tax on parts only. My vehicle has only 78,000 miles of only city and freeway driving. Would this be an average repair needed for this type of driving and is this price in the right area? Also what parts are included in a strut assembly?