Scientific notation is a way of writing very big or small
numbers. In scientific notation, a number can look like
“−2 * 10^{−3}”. To write this the
usual way, you take the first number (−2) and move the
decimal point the number of places given by the superscript
(−3). (The 10 is always there; you can ignore it.) Of
course, −2 was written without a decimal point, but it's the
same thing as −2., so we move the decimal point of
−2. three places to the left. (If we had 3 instead of
−3, we would move it three places to the right.) Moving one
place gives −0.2, moving two places gives −0.02 and
moving three places gives −0.002, so that's our answer.

If the exponent is 0, then you don't need to move the decimal
point at all! So −8.6 * 10^{0} is just −8.6.