Radicals and complex numbers

[GypsySkies]

Instructions say: Simplify the expressions. Write the answer with positive exponents only.
The problem:
(1/16) Exponents:-3/4 - (1/8) Exponents: -2/3
I worked it:
(1/16 to fourth power) Exponent: -3 - (1/8 to third power) Exponent: -2
(1/2) Exponent: -3 - (1/8) Exponent: -2
-1/8 + 1/4
-1/8 + 2/8
1/8

The answer is 4. I'm really not sure what I did wrong.

 

[Denis]

(1/16) Exponents:-3/4 - (1/8) Exponents: -2/3

Use ^ for exponent:
(1/16)^(-3/4) - (1/8)^(-2/3)

Hint: a^(-x) = 1 / a^x