We are given the equation:
\[
\frac{dx}{dy} + 2y = e^{3x}
\]
This is a first-order linear differential equation. To solve this, we can use an integrating factor. Rearrange the equation into standard linear form:
\[
\frac{dx}{dy} = e^{3x} - 2y
\]
This equation suggests that the solution will involve an exponential form related to \( e^{3x} \), and we expect the general solution to be of the form \( e^{3x} \) since this is the main exponential term in the equation.
Thus, the correct solution is:
\[
\boxed{e^{3x}}
\]