$\displaystyle \frac{dz}{dt} + 3e^{t+z} = 0$

Here's what I have done:

$\displaystyle \frac{dz}{dt} = -3e^{t+z}$

$\displaystyle \ln(dz) - \ln(dt) = \ln(-3) + ln(e^{t+z})$

Am I approaching this correctly? Something is obviously wrong since the ln(-3) is undefined, which makes me think that I am doing this wrong.

Thanks!