Is it realistic of me to lose weight in 6 weeks?

In August, my partner will be going overseas to visit her family. While she's gone, I want to work on losing weight. Currently my pants size is 36W, and I want to go down to at least a 30W. Is this realistic? I've never been one for exercise, but I really want to get in better shape while she's gone to surprise her. Is this a realistic goal? Or should I aim for less?

I'm 5'4" and about 180lbs. I've been steadily trying to lose weight by walking, but I don't think just cardio is helping.