To write the radius of Neptune, approximately 15,300 miles, in scientific notation, we want to express it in the form \( a \times 10^n \) where \( 1 \leq a < 10 \) and \( n \) is an integer.
The number 15,300 can be expressed as:
1.53 (which is between 1 and 10) multiplied by \( 10^4 \) (since you move the decimal point 4 places to the left to turn 15,300 into 1.53).
Thus, in scientific notation, it is written as:
\[ 1.53 \times 10^4 \]
So, the correct answer is:
1.53 x 10^4.