Can anyone help?

What I want to do is enable a figure in column B to be shown if column L is
filled in with a date.

Eg. if L35 has a date in the cell, the figure in B35 is to appear. I want
this rule for every cell lin column B and L.

Eg. If (L35=date, then use figure in B35) + If (L36=date, then use figure in
B36) etc. etc. = total number.

Can anyone help?