16 boards that are 5.7 inches wide each make a total of 91.20 inches.
16
x 5.7
112
+800
91.2 inches
Since the deck itself is 94.45 inches deep, we can subtract 91.2 from the number:
94.45
-91.20
3.25 inches.
Finally, we divide 3.25 by 15, since that's the amount of spaces we want and they have to be equal:
3.25/15= .21667
We'll round that to two numbers, so we'll end up with .22.
Your final answer is .22 inches wide for each space.