Determine the equilibrium solution (D₁ = S₁, D₂ = S₂) of the two-commodity market with linear model (D, S, P = demand, supply, price; index 1 = first commodity, index 2 = second commodity)

D₁ = 40 - 2P₁ - P₂,    S₁ = 4P₁ - P₂ + 4,
D₂ = 5P₁ - 2P₂ + 16, S₂ = 3P₂ - 4.