On the second day, the company paved 4 * 2 - 1 = <<4*2-1=7>>7 miles.
The company has 16 - 7 - 4 = <<16-7-4=5>>5 miles of road remaining to pave.
They will need 3 * 5 = <<3*5=15>>15 truckloads of asphalt to pave 5 miles of road.
For 15 truckloads, they will need 15 * 2 = <<15*2=30>>30 bags of gravel.
Thus, the company will need 30 / 5 = <<30/5=6>>6 barrels of pitch to finish the road on the third day.
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