Answer:
 50.5mL
Step-by-step explanation:
Given parameters: 
Initial volume of coke V₁ = 25mL 
 1 atm = 101.325kPa
Initial pressure on coke P₁ = 100kPa = 0.99atm
Final pressure on top of mountain = 50kPa = 0.49atm
Unknown: 
Final volume = ? 
Solution: 
To solve this problem, we simply apply Boyle's law. 
Boyle's law states that "the volume of a fixed mass of gas is inversely proportional to pressure provided that temperature remains constant". 
Mathematically; 
 P₁V₁ = P₂V₂
where P and V are pressure and volume. 1 and 2 are initial and final states. 
Input the parameters and solve for V₂; 
 0.99 x 25 = V₂ x 0.49
 V₂ = 50.5mL