To add the numbers \(5.75 \times 10^4\) and \(3.81 \times 10^4\), you can combine the coefficients since they have the same power of ten:
\[ 5.75 + 3.81 = 9.56 \]
So,
\[ 5.75 \times 10^4 + 3.81 \times 10^4 = 9.56 \times 10^4 \]
Thus, the answer is:
\[ 9.56 \times 10^4 \]