2x108 3x72 4x54 6x36 8x27 9x24 12x18 18x12
The answer depends on the units used for 6*36. It also depends on the shape of the 40 square feet area. If it is a circular shape then a lot of tiles will need cutting and that will result in a significant amount of wastage.
Buy what you want but here are some suggestions. the SMK 6x36 35mm dayscope, red dot laser aimer, bipod, susat sight, acog sight, red dot sight and finally if you have £15,000 to spend, a BW thermal scope.
First, find the square footage of a 6" x 36" plank. 6 x 36 = 216 square inches. There are 144 square inches in a square foot (12" x 12" = 144). So divide 216 by 144 to get the square feet per plank. 216 / 144 = 1.5 sq ft per plank. Your room is 16' x 12'. Multiply the two numbers to find square footage of the room: 16 x 12 = 192 square feet. You have 192 square feet, using planks that are 1.5 sq ft each. 192 / 1.5 = 128 planks. Generally, you will want to add from 5% to 10% for waste, depending on your layout (is it one big room, or several smaller rooms with lots of cutting?) (are you doing a straight layout, or diagonal?) and your skill level. If in doubt, add 10% to be safe. 128 planks + 10% --- that's 128 x 1.1 = 140.8 planks.