About 14 bricks should do it.
A lot !!
The first step is to convert the total patio area to inches so we are working with the same units. 100sq ft = 14,400 sq inches. Now we need to calculate the number of square inches each brick takes up. Answer: 36 sq in. Now we just divide the total square inches of the patio by the square inches taken up by each brick: 14,400/36 = 400 bricks. It will take 400 bricks to make a 100 square foot patio.
1,350 of them.
Gee, a square foot is 12x12, difficult problem.
The question, as stated cannot be answered. You need to know two dimensions of the bricks to find the area of each brick, convert that area into square feet (if necessary) and then divide 256 by the area of each brick. Bricks are not usually square so it would not be appropriate for me to assume that the bricks are 16" by 16".
2700 4" x 8" bricks (plus 10% waste)
use a pressure washer