Answer:
The answer to your question is P1 = 1.4 atm
Explanation:
Data
Volume 1 = V1 = 735 ml
Pressure 1 = P1 = ?
Volume 2 = V2 = 1286 ml
Pressure 2 = P2 = 0.8 atm
Process
To solve this problem use Boyle's law.
     P1V1 = P2V2
-Solve for P1
     P1 = P2V2 / V1
-Substitution
     P1 = (0.8 x 1286) / 735
-Simplification
     P1 = 1028.8 / 735
-Result
     P1 = 1.4 atm