Find the derivative of f(x) = negative 5 divided by x at x = 11.

I want to believe the equation is,
 f(x) = -5/x
This can be written as;

f(x)  = y

y = -5 x⁻¹
derivative = dy/dx = (-1)(-5)x(⁻1-1)
                              = 5x⁻²
 
Derivative at x=11, 

dy/dx = 5(11)⁻²
         = 5/(11²)
         = 5/121

So, the derivative of  f(x) = -5/x at x=11 is 5/121.