For a, assuming that you will be spraying all sides of the cushions, including the side facing down, you need to figure out the total surface area for the cushion. The formula is 2(lw + wh + hl). l = length, w = width, h = height. Once you do that, then you will need to multiply that number by six because there are six cushions. This number will be in sq. centimeters. Next you need to convert the coverage area of the spray from sq meters to sq centimeters ( m = 1000cm). Now you will take your total surface area of the six cushions and divide it by the number of sq. centimeters that one can of spray covers and that will give you the number of cans needed.
For b, you will take the number of sq centimeters per a can and multiply by 10% (.10), then add that number to the original can amount. Now you will take the total surface area of the six cushions and divide it by the 10% more amount you just calculated to find out how many cans are needed. This answer should be a smaller number than the number of cans calculated for answer a.
