To subtract \( 5.9 \times 10^4 \) from \( 13.5 \times 10^6 \), we need to express both numbers with the same exponent.
We can rewrite \( 13.5 \times 10^6 \) as \( 13.5 \times 10^6 = 13.5 \times 10^6 \), and convert \( 5.9 \times 10^4 \) into the same exponent as \( 10^6 \).
To do this, we convert \( 5.9 \times 10^4 \) to \( 10^6 \) by multiplying and dividing by \( 10^2 \):
\[ 5.9 \times 10^4 = 5.9 \times 10^4 \times \frac{10^2}{10^2} = 5.9 \times 10^{4 + 2} = 5.9 \times 10^6 \times 10^{-2} = 0.059 \times 10^6 \]
Now we can subtract:
\[ 13.5 \times 10^6 - 0.059 \times 10^6 = (13.5 - 0.059) \times 10^6 = 13.441 \times 10^6 \]
Finally, this result can be expressed in proper scientific notation. Since \( 13.441 \) is between 1 and 10, we convert it to:
\[ 1.3441 \times 10^7 \]
Therefore, \( 13.5 \times 10^6 - 5.9 \times 10^4 \) in scientific notation is:
\[ \boxed{1.3441 \times 10^7} \]