Solve the following linear programming problem using its Dual form:
Minimize Z = 3x₁ + 4x₂
Subject to:
4x₁ + x₂ ≥ 30
-x₁ - x₂ ≤ -18
x₁ +3x₂ ≥ 28
where x₁, x₂ ≥ 0