Timesheet to calculate hours, subtract lunch, and calculate overtime hours

Good afternoon! This is my first post.

I am looking for a timesheet template that allows me to enter start/end times for employees and then calculate hours worked. From that, I want to subtract a "lunch" - usually 30min - to determine hours worked. From that, I need to determine how many of those hours worked are standard and how many are overtime.

I started the attached but F2 gave me an error trying to subtract the 8 regular hours from the 12 hours to determine the overtime hours (which would go in cell G2). E2 should be 11.5...but I can't get that to work.

I know this is so elementary but I would appreciate the help.