Say your individual bill total is in Column D, from D2 on down.

In E2, enter this formula:

=D2/4

Now click back in E2 to select it.

In the lower right hand corner of that selected cell you'll see a small
black square.
Hover your cursor over that square until it changes from a fat white cross
to a skinny black cross.
Then click and drag down as many rows as you think you'll need.
This *automatically* copies the formula for you, so that you don't have to
enter it yourself in each individual cell.