What is 0.00086 in scientific notation?
For numbers that follow zeros to the right of the decimal, you start to the right of the first non-zero digit and place the decimal there.
Then you count the number of digits between the original decimal and the new decimal. This number is the exponent on 10.
Now you have all the information you need. First you put the number you created in the first part (8.6), then you multiply it by 10exponent.