Density is simply mass divided by volume or m/v. So, here you have 1.15 kg/3.8 deciliters = 0.303 kg/dL = density.
However, most chemists prefer density in units of g/ml or kg/L, etc. So, to convert to the more general g/ml, you must convert kg to g and dL to ml.
0.303 kg x 1000 g/kg = 303 g
1 dL x 100 ml/dL = 100 ml
Density in g/ml = 303 g/100 ml = 3.03 g/ml