Can you replace the question mark with the correct number?

The answer I give is yes, but what I mean is no. What was the question?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

O_er_t_o_

Complete the missing letters of the given word.

Our product and our sum always give the same answer. Who are we?

To attend world science seminar, A famous chemist from Mexico visit
London. In the lab, the scientist was killed and his six assistants were under suspicion of killing the chemist.
Name of six assistants: Austin, Wayne, Dege, Oscaru, Lingard, and Rojo.
He left a note "76-20-44 79-16-22-7"

A local detective Jack was called to solve the case,

After reading the note, Jack instantly asked the police to arrest the murderers.

Who are the murderers?

You see me once in June, twice in November, and not at all in May. What am I?

What part of the chicken has the most feathers?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

What does below pictogram mean?