We first consider the ideal gas equation,
PV = nRT
It is stated that the pressure and temperature are constant; moreover, R is already a constant. So, we get:
V = constant * n
This is the equation of direct proportion. Therefore, we get:
V/n = constant
V₁/n₁ = V₂/n₂
Substitute the values and solve for V₂
V₂ = (4 * 1.48) / 0.864
V₂ = 6.85
6.85 Liters of gas must be present at the end, so we need to add:
6.85 - 4 = 2.85 liters