help with simple addition formula
 

The formula below I am using to add 3 cells. I would like it to add M8 in to
the addition only if M7 is blank. How do I adjust my formula to do this?

M7+M13+M14

thanks

Juco wrote:
Not quite working for me, Maybe the bit below will explain better. I need
to add up M13 M14 in M15 then either M7 or M8 M7 is a weekly rental cost
M8 is a total rental cost Some people might just fill in the weekly if
only renting for one week and leave the total blank, hence the reason i want
to pick up either or of M7 and M8. M8 if they have put the total in if not
then M7.
Hope I am not getting confusing now


Weekly rental M7
Total rental M8
Airport transfer req.
Yes or No no
Welcome pack req.
Yes or No no
Transfer cost return M13
Welcome pack M14
Total rental M15
[...]

Perhaps...

=SUM(M13:M15,IF(N(M8),M8,M7))