The answer depends on the units of measurement used for the numbers in the question: feet, metres, centimetres, miles, etc.
You get the answer by multiplying length and width. This calculation gives you 81 square feet.
90
Assuming 9x9 is also in feet, then answer is 81 square feet.
141.75
If it is nine feet by nine feet, then it is 81 square feet.
16 if there is no wastage or cutting.
To turn a 9x9 square into an octagon you can cut corners off the square. It will not be a regular octagon though.
81
Each tile covers 81 square inches. You have 1,296 square inches to cover. It will take 16 tiles to cover that area.
81 (9x9) & 9 (3x3)
A 9x9 foot slab 4 inches thick requires a minimum of 1 cubic yard. If you go to 6 inches thick you will need 1.5 cubic yards.
9x9=81
Volume = length * width * height. (The * is a 'multiply' sign). So, 16.2 feet* 9.8 feet* 8 feet = the answer in cubic feet. This is how to solve the problem. If you need a calculator, windows has one (or Google will act as one.)