Surds, Indices and Logarithm

What is the value of x in the equation log_x(1/81) = 4

There are 10 true false questions in an examination. These questions can be answered in -

If √2ⁿ = 64 , what will be the value of n? 

(5³ + 5³ + 5³ + 5³) = ?

The solution to log₂x = 5 is: