so for a) the question is asking you to express 27^1/2 as a number raised to a power i.e. x^y. here you have been given x as 3.
so 27^1/2 is the same as (3^3)^1/2 which is the same as 3^(3^2)
sorry dont know how to type in mathematical equations but if you write the above on paper, hopefully it will make sense.