414.48 square feet is needed to make 3 dozen of the covers.
To find the circumference, you multiply the 4 by π, and π is 3.14, and you get 12.56.
The 12.56 is literally the length of the side. The width is the height of the cover which is 10 inches. 12.56 multiplied by 10 is 125.6 square inches.
Step 3: Add them up.
125.6 + 12.56 is 138.16
138.16 multiplied by 36 is 4973.76 square inches.
12 inches is 1 foot so we divide 4973.76 by 12. You get 414.48 square feet.