Which expression is equivalent to the following function?

Answer 

B. f(x) = - (y/x)⁵

Explanation
A negative power means the reciprocal of that number raised to the positive value .
For example, a⁻ⁿ = 1/aⁿ

So, for the question above.
f(x) = -(x/y)⁻⁵
      = - 1/(x/y)⁵
      = - (y/x)⁵

The answer for the problem shown in the figure attached, is the option B, which is:
 B) f(x)=(-y/x)^5
 The explanatio for the exercise is shown below:
 1. You have the following function given in the problem above:
 f(x)=-(x/y)^-5
 2. The negative exponent -5, indicates that the x must be in the denominator and the y must be in the numerator, and the exponent must be positive as following: 
 f(x)=(-y/x)^5