It was 10 1/2 feet long before it was cut, and the s/he cut out 3 3/4 feet. We are calculating for how long is left after it was cut, so you would take 1/2 and make its denominator into 4. Now, you have 2/4 minus 3/4, and that would be -1/4. You will use 10 and subtract 3, which you get 7. Since it says negative 1/4, you can use one whole number, change it to 4/4, and it would get you 3/4. Now, since you used one of the whole numbers, it would be 6. Your answer will be 6 3/4.
Complete answer: "The remaining piece of the board is 6 3/4 feet long.