Here's how we get there:

* Move the decimal: Start with the decimal point at the end of the number (300,000,000.) and move it to the left until it is after the first non-zero digit (3.). You moved it 8 places to the left.

* Exponent: Since you moved the decimal to the left, the exponent is positive and is equal to the number of places you moved it (8).

* Result: 3 x 10⁸