what is the density of a substance if a 2.50 ml sample has a mass of 0.880g at room temperature? what is the specific gravity of the substance?

density = mass/volume

Specific gravity is the same number (but no units) if you assume density of H2O = 1.00 g/mL. If you know the density of H2O at room T (I don't know what you're calling room T) then
sp.g. = density substance @ T/density H2O at same T.