you need to calculate the square feet of the ceiling, so you multiply the dimensions of the ceiling.
35(40)=1400ft^2
now, you know that for every 100 square feet you need a specific # of pots, so you divide 1400 by 100.
1400/100=14
now we know that there are 14 areas of 100 where you can place 2-3 pots.
so, you multiply 14 by 2 & by 3
14(2)=28
14(3)=42
so you know that you can have between 28-42 pots.