The Figure Above Shows the Market for Shirts in Australia

The figure above shows the market for shirts in Australia, where D is the Australian demand curve and S is the Australian supply curve. The world price is $20 per shirt. Australia imposes a tariff on imported shirts of $4 per shirt.
-In the figure above, the tariff _______ Australian imports of shirts by _______ million shirts per year.

A) decreases; 8
B) decreases; 16
C) increases; 4
D) increases; 8