If we assume that none of either liquid is lost in the process, and the
'spoonful' is an exact measure, then the volumes in the two containers
after the transfers are the same as before having had a spoonful added
and removed.
Then whatever amount is missing from the coffee cup must be in the tea
cup. Let's say 10ml of coffee is missing from the coffee cup. But the
10ml of coffee must be displacing 10ml of tea from the tea cup which
must, therefore, be in the coffee cup. The actual amount, of course, is
not relevant. Dave Abineri