Is this normal?

Deanna
So we booked our venue, and when I went in to sign the invoice, and I got confused. In their book it says they add a 18% gratuity for waitstaff, which I am totally okay with. However the gratuity added to my invoice is close to 34%, and then they added a sales tax to the gratuity. I'm getting married in June, 2015 in McAllen, texas. I want to go talk to them because I feel like it isn't right. Any advice or anything?