My school teacher, has asked the above question in the spirit of Science Fortnight.
However, he has only left the following on the whiteboard:
Clue 1:
8, 6, 7, 9, 5, 6, 8, 6, 8, 4, _.
Clue 2:
$19 = 21 \times \_ + \frac{1}{2}\times 1 \times \_^2$
(Reverse your answer)
$\times$ represents standard multiplication $\_^2$ is a number to the power of two.
Clue 3:
212, 113, 43, 35, 32, 27, 25, _
What is my teacher's favourite animal?
Hint:
Clue 1 - Chemistry
Clue 2 - Physics
Also - you can solve both of these without any maths. The maths tag was for Clue 3.
Hint 2:
You should get a single number from putting the numbers from each of the clues together in some arrangement. This single number corresponds to an animal.