Adding the zip code to the contact form

Hi! On the website that I am doing for my client: Insured Life Of Georgia, I added a text field on the front right sidebar where a prospective client enters in the zip code from where he/she is from before it takes him/her to the application form (from contact form 7)to fill out.

The question is how can I save the zip code from what the prospect entered so when my client receives the email, not only he sees the application form, but the zip code as well?

I would greatly appreciate this. Thanks!