HELP!!

I'm working on a project for my class and they want me to "test whether
there is a value in a cell in order to sum it up"

Add Invoice total + Shipping Cost + Sales Tax.

However, the Shipping Cost Cell has been set up as follows:

=IF(H14="","---",IF(OR(H14="ID",H14="OR"),"NO
COST",IF(H14="NV",O27*0.6,IF(H14="CA",O27*0.9))))

So if there is "NO COST" in the Shipping Cost cell the simple summation
formula won't work. They want us to do ISTEST, but I can't find any
information on this. I am beginning to think its a typo.

Any advice would be great!