I assume the underlined digit tells you to round off to that place. In this case, the 3 is in the tenths place, so you need to round off 2.348 to the nearest tenth.
2.348
The 3 is in the tenths place. If you are asked to round off to the nearest tenth, then first, drop the digits to the right of the 3. Now you have 2.3, but we need to look at the next digit in the original number. The original number was 2.348, with a 4 to the right of the 3. Since 4 is less than 5, you just keep the rounded number as 2.3.
Answer: 2.3