A bit-stuffing based framing protocol uses an 8-bit delimiter pattern of…

Key insight: after any sequence of five consecutive 1s in the original data, a 0 is inserted (stuffed). To recover the original input, remove any 0 that immediately follows five consecutive 1s.

• Step 1: Scan the stuffed output 01111100101 and find a run of five 1s followed immediately by 0. Here the substring 11111 is followed by a 0.

• Step 2: Remove that stuffed 0. Removing the 0 after the five 1s turns 01111100101 into 0111110101.

Therefore the original input bit-string is 0111110101.