Can you explain this question?

#1

please explain this question.

#2

suppose u are given a = 1 and b = 2 and n=3
you are supposed to form all the 3 digit numbers which have 1 and 2 but without consecutive 2s
for eg: 111 or 112 or 121 or 211 and 212 are valid numbers but 221 122 222 are invalid

#3

hey @raj.verma5454 if your doubt is solved, please mark it as resolved