1 Foot has 12 inches.
Since the privacy fences are 8 foot long.
Multiply 8 with 12 to find the total inches required which comes out to be 96 inches.
Since fence slats are 6 inches, divide 96 by 6 to find your answer which comes out to be 16.
Thus you require 16 fence slats to make 8 foot long privacy fences.
Hope this helps!