6.45 x 10^5
In scientific notation, the coefficient must be between 1 and 10.
To convert a number in which the coefficient is greater than 10, you
1. Move the decimal point enough places to the left to make the coefficient between 1 and 10
2. Increase the exponent by the number of places you moved the decimal point
In the coefficient 64.5, you must move the decimal point one place to the left to get 6.45 (a number between 1 and 10), so you increase the exponent by one.
Thus, 64.5 x 10^4 = 6.45 x 10^5
