Answer:
3.85L
Step-by-step explanation:
Given parameters: 
Initial pressure P₁ = 15psi (1psi = 52mmHg)
 converting to mmHg gives (15x52)mmHg = 780mmHg
Initial volume V₁ = 7.0L
Final pressure P₂ = 1420torr= 1420mmHg
Unknown: 
Final volume V₂ = ? 
Condition of the process: Constant temperature
Solution
To solve this problem, we simply apply Boyle's law. Boyle's law states that "The volume of a given mass of gas varies inversely as the pressure changes, if the temperature is constant". 
It is mathematically expressed as ;
 P₁V₁ = P₂V₂
The unknown here is V₂ and we simply express it as the subject of the formula: 
 V₂ = 
 
 
 V₂ = 
 
 
 V₂ = 
 = 3.85L
 = 3.85L