The gas arsine (AsH3) decomposes as follows: 2AsH3(g) 2As(s) + 3H2(g) In an experiment pure AsH3(g)

Question:

The gas arsine (AsH3) decomposes as follows:
2AsH3(g) ⇌ 2As(s) + 3H2(g)
In an experiment pure AsH3(g) was placed in an empty, rigid, sealed flask at a pressure of 392.0 torr. After 48 h the pressure in the flask was observed to be constant at 488.0 torr.
a. Calculate the equilibrium pressure of H2(g).
b. Calculate Kp for this reaction.