You need to find the total surface area of the rectangular prism. The top and bottom are 8(6), which equals 48. Since we want both the top and bottom, multiple 48 by 2 to get 96. The we need to calculate the remaining 4 sides. Two of them are 15(6), which is 90. Again, multiply by two since there’s two of those sixes to get 180. Finally, the last two sides are 15(8), which is 120. Add all of these numbers together to get 96+180+120=396. So she will need 396 cm^2 of fabric.