Simplify:
Which of the following is equivalent to $\frac{(frac{1}{t}$-$\frac{1}{x}$)}{x-t} ? Assume that denominators are always nonzero.
t-x
$x^{2}$$-t^{2}$
$\frac{x}{t}$
x-t
$(xt)^{-1}$
