Time sheet calcs Help!

Hi there.
This is my first post and hoping to get a direction to my time sheet. (attached)

Im ive got the first day setup how I want it, with task, start time , finish time, and staff member.
But I am now at a loss for creating the necessary formulas for calculations (and cell formatting) to calculate staff hours.
As you can see below the calender, I have the staff names and some basic attempts of formulas (but just the first step, for hour calcs), all coming up with errors.
Why cant my formulas calculate hours?
Can anyone help?

Kind regards
Neil