How do you rewrite expressions using a positive exponent when the exponent originally attached is negative/fraction?

Autility company burns coal to generate electricity. the cost c(p), (in dollars) of removing p percent of the some stack pollutants is given by c(p)= 85000p/100-p a) find the cost to remove 30% of the pollutant b) find where the function is undefined

Evaluate-27 ^4/3/8 a) - 81/16 b) 81/16 c) 16/81

Evaluate cos2θ for cosθ = square root of 3/2