its base 15 means . the system will have 15 number - 0 to E. And 15 is represented as F . so it is asking the radix complement of the number, now the radix complement can be written as dimnishd radix complement + 1.
so dimnished radix biggest number of n digit - number.
here biggest digit is e . so
eeee- 3a2e = b4c0
radix will be b4c0 + 1 = B4C1