Basic thermophysics question

This shouldn't be too difficult, I just can't get it right for some reason.

"An old bathtub has a hot water tap, and a cold water tap. The hot water tap can be used to fill the whole bathtub up with 78 ºC-water in 13 minutes. The cold water tap can fill the bathtub tab up with 10 ºC-water in 19 minutes. What's the final temperature going to be, if both the hot and cold water taps are used simultaneously until the bathtub is full?"

Water has the heat capacity 4180 J/(kg*K) just in case you don't remember. Anyway, the only thing I could think of was to add the times it takes to fill up the bathtub together, then dividing the individual times with those values to get a percentage-value, but it didn't provide an accurate result either for the end temperature.