When working with decimals, you should write in missing decimals.
If you do not see a decimal, it is at the end of the number.
When adding decimals, you need to line up the decimals so that they are in the same place.
2.9 + 35.1 + 7.68
45.68 Keep the decimal in the same place.
When multiply decimals, count the amount of digits behind the decimal, put that amount of digits behind the decimal in your answer. Start counting from the right, if there are not enough digits place an appropriate number of zeros in the front.