(a) At 298 K, butane follows the equation of state: P(V - b) = RT at moderate pressures, where b is a function of temperature. Calculate the fugacity for butane at a temperature of 298 K and a pressure of 1 MPa. At this temperature, b = -732 cm³/mol.

(b) Pentane follows the same equation of state with b = -1195 cm³/mol at 298 K. In a mixture, b follows the mixing rule: b = x₁b₁ + 2x₁x₂b₁₂ + x₂² b₂ where b₁₂ = -928 cm³/mol. Calculate the fugacity of butane in a 20 mol% concentration in pentane at 298 K and 1 MPa, assuming the mixture is an ideal solution.