You may want to review understanding scientific notation first.
To rewrite a number in scientific notation, you need to work out the first number and the superscript. The first number will be the same as the number you're given, except the decimal point will be just to the right of the leftmost non-zero digit. For example, if you're given −54000, the first number will be −5.4. (You could write it −5.4000, but that would be silly.) To find the superscript, count how many places you needed to move the decimal point. In this case, to get from 54000 to 5.4 we needed to move the decimal point four places to the left. So the superscript is 4. (If we had had to move it to the right, then the superscript would have been −4.). So the final answer is −5.4 * 10−4.