So then it looks like you have no say in the design of the structure.
Then you have two options.
1. IIF (and Embedded IIF)
2. Create A Public Function
IIF (Assumes only one can be true)
Query Field
=IIF([Chk25]=True,25,IIF([Chk15]=True,15,IIF([Chk10]=True,10,0)))
(Assumes any could be...