In 1623, the unit digit of base 16 is 6 and the power is 23 (odd power).
Therefore, unit digit of 1623 is 6.
In 7148, the unit digit of base 71 is 1 and the power is 48 (even power).
Therefore, unit digit of 7148 is 1.
Also in 5961, the unit digit of base 59 is 9 and the power is 61 (odd power).
Therefore, unit digit of 5961 is 9.
Sum of the unit digits = 6 + 1 + 9 = 16
∴ Unit digit of the given expression is 6.