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A model of a Delta IV Medium+ (5,4). No scale was noted on the plaque.

The "5" indicates a 5 meter diameter payload fairing (rather than the standard 4 meter fairing) and the "4" indicates the use of four strap-on GEM-60 graphite-epoxy solid rocket motors (although only two actually appear on the model, leading me to believe that this is actually a Delta IV Medium+ (5,2)).