The density of a substance with a mass of 48 grams and a volume of 3 ml is what

P = m/v
Where P is the density,
m is the mass (in g), and
v is the volume (in L)

P = m/v
= (48 g)(0.003L)
= 0.144 g/L

Significan figures count too.
48 g has two significant figures
0.003L has to only one significant figure. Therefore, the answer will have only 1 significant figures.
Our final answer will be 0.1g/L

The mole ratio of hydrogen to ammonia is 3: 2.