Hard Puzzles 

Workings

Hint
A tricky base 8 question.

Answer
61.

Each term is a square expressed in base eight, 7 2=49 = 61 in base 8.

Workings

Hint
Look to the skies.

Answer
TH.

The last two letters of the planets in reverse order from the sun.

Workings

Hint

Answer
1680.

This is n to the power of 5, starting with 2^5 = 32, with the last digit missing, 7^5 = 16807.

Workings

Hint
A very common sequence is hidden here.

Answer
Badger.

Reasoning
The length of the words is the same length as the months of the year.
   gorilla  = 7 = January
   hedgehog = 8 = February
   camel    = 5 = March
   mouse    = 5 = April
   fox      = 3 = May
   bear     = 4 = June
   mole     = 4 = July
   badger   = 6 = August