If you would like to know what length of the board was cut off, you can calculate this using the following steps:
12 3/4 feet long board - 9 7/8 feet = 12 3/4 - 9 7/8 = 51/4 - 79/8 = 102/8 - 79/8 = (102 - 79) / 8 = 23/8 = 2 7/8 feet
The correct result would be B) 2 7/8 feet.