You've kind of answered your question already.
Thermal energy, U, is equal to the heat capacity times the temperature:
U = CT
We can assume the tea and water in the bathtube have the same specific heat capacity, which is the heat capacity divided by the mass. (Under what conditions might this not be a good assumption?).
Therefore you need to estimate the quantity
[tex]\frac{U_{tea}}{U_{tub}}[/tex]
You'll need to estimate volumes (masses) for the tea and the tub.