How many asphalt strip shingles that measure 3′ x 1′ wide will it take to cover a square of roof with a 4/12 pitch? The shingle exposure is 4 1/2″.

How many asphalt strip shingles that measure 3′ x 1′ wide will it take to cover a square of roof with a 4/12 pitch? The shingle exposure is 4 1/2″.