If we round a number to the nearest tenth then we have to write it with only one decimal digit i.e. with only one digit at the right of the dot. The digit in this place depends on the value of the digit at its right. If this is equal or greater than 5 then the we have to add 1 to the digit at the right of the dot. In any other case the digit right next to the dot remains unchanged. For example, in 12.86 we need to take the last digit in order to round it to the nearest tenth. However, this digit is greater than 5 so we also need to add 1 to the digit at the right of the dot:
In 6.147 we need to erase the second and third digit after the dot. Here the second digit is smaller than 5 so the first digits remains unchanged. Then we get:
Then we can find our estimation:
Then the answer is 6.8.