A few extraterrestrials arrived. They had two hands, however claimed that 5+4=11 . How many fingers did they have on their two hands? Note that our decimal system (and ten characters: 0, 1, 2, 9) certainly has its origin because we have ten fingers.
[Hint: 11 are in their system. In our decimal system, the result would be written as 5.]
Express your answer as an integer.