Answer: The first bolt he bought is 7/8 inches long. The second bolt he bought is 5/8 inches long.
Explanation:
The bolt he already has: 3/4 inches, or this can be written as 6/8 inches.
Since the the first bolt he bought was 1/8 inches longer than the original one, we can do 1/8 + 3/4 (6/8) and we get the sum of 7/8.
The first bolt he bought is 7/8 inches long.
The second bolt he bought was 1/8 inch shorter than the first one, so we just take 1/8 from 3/4,
==> 6/8 - 1/8 = 5/8
The second bolt he bought was 5/8 inches long.
Hope this helped, have a good day :D