This is an incomplete question, here is a complete question.
Hydrogen azide, HN₃, decomposes on heating by thefollowing unbalanced reaction:

If 3.0 atm of pure HN₃ (g) is decomposed initially,what is the final total pressure in the reaction container? Whatare the partial pressures of nitrogen and hydrogen gas? Assume thatthe volume and temperature of the reaction container are constant.
Answer : The partial pressure of
and
gases are, 4.5 atm and 1.5 atm respectively.
Explanation :
The given unbalanced chemical reaction is:

This reaction is an unbalanced chemical reaction because in this reaction number of hydrogen and nitrogen atoms are not balanced on both side of the reaction.
In order to balance the chemical equation, the coefficient '2' put before the
and the coefficient '3' put before the
then we get the balanced chemical equation.
The balanced chemical reaction will be,

As we are given:
The pressure of pure
= 3.0 atm

From the reaction we conclude that:
Number of moles of
= 3 mol
Number of moles of
= 1 mol
Now we have to calculate the mole fraction of
and 

and,

Now we have to calculate the partial pressure of
and 
According to the Raoult's law,

where,
= partial pressure of gas
= total pressure of gas = 6.0 atm
= mole fraction of gas


and,


Thus, the partial pressure of
and
gases are, 4.5 atm and 1.5 atm respectively.