How to zero or keep calculated value in a cell based on text in another cell in same row

[Geosele]

In snapshot below...the Fees in cell are by a calculation eg "=C2*10" assuming £40 and PAID Yes/No (is as dropdown) are in Row C2 too.
QUESTION 1: If PAID is Yes, then keep the Fees value. If the PAID is changed to No, then the Fees is ignored and a "£0:00" value is inserted.
QUESTION 2: I would then like to add all PAID (Yes) and show the running TOTAL PAID fees at botton/end of spreadsheet.
Thanks in advance.

 

[Geosele]

Query update with new snapshot

 

[p45cal]

Q.2: In a cell, something like:
=SUMIF(D2:D34,"Yes",C2:C34)
which may make Q.1 redundant.

 

[Geosele]

Thanks alot p45cal