Apply principle of duality to solve LPP

Question

Apply principle of duality to solve the LPP.
Minimize Z=2x1 + 2x2
Subject to,
2x1 + 4x2 ≥  1
x1 + 2x2 ≥ 1 

2x1 + x2 ≥  1
x1, x2 ≥  0