To find out how much farther Neptune is from Earth than Mars, we need to subtract the distance to Mars from the distance to Neptune.
- Distance to Mars: \( 2.25 \times 10^8 \) km
- Distance to Neptune: \( 4.3514 \times 10^9 \) km
To perform the subtraction, we should first express both distances with the same power of 10.
Rewriting \( 4.3514 \times 10^9 \) km in terms of \( 10^8 \):
\[ 4.3514 \times 10^9 = 4.3514 \times 10^1 \times 10^8 = 43.514 \times 10^8 \]
Now we can perform the subtraction:
\[ 43.514 \times 10^8 - 2.25 \times 10^8 = (43.514 - 2.25) \times 10^8 \]
Calculating \( 43.514 - 2.25 \):
\[ 43.514 - 2.25 = 41.264 \]
Now express this in scientific notation:
\[ 41.264 \times 10^8 = 4.1264 \times 10^9 \]
Thus, the distance that Neptune is farther from Earth than Mars is:
\[ \boxed{4.1264 \times 10^9} \text{ km} \]