I used the suggested function =IF(ISNA(C81),"0",C81) which worked fine.
However, the following formulas resulted in an answer of "0" which was
incorrect. The last formula did not recognize that a value was greater than
zero.

value in B12 is 99.506
value in C12 is #N/A
value in D12 is #N/A

F12 is =IF(ISNA(B12),"0",B12) this returned 99.506
G12 is =IF(ISNA(C12),"0",C12) this returned 0
H12 is =IF(ISNA(D12),"0",D12) this returned 0
I12 is =IF(F12G12,F12,G12) this returned 0 when it should be 99.506

Where did I get off track?