You may want to review positive exponents first.

Multiplying by something raised to a negative power is the same
as dividing by the same thing raised to the positive power. For
example, multiplying by *a*^{−2} and dividing
by *a*^{2} are the same thing. So, if you have to
simplify
(−2 ⁄ *a*^{2})(−1)^{0}(*b*^{2} ⁄ *a*)^{−2},
you can rewrite it as
(−2*a*^{−2})(−1)^{0}(*b*^{2}*a*^{−1})^{−2}.
(Remember that *a* is the same as *a*^{1}, so
dividing by *a* is the same as multiplying
by *a*^{−1}.) By what you already know, this is
the same as −2*b*^{−4}. But you want to
write your final answer without negative exponents, so you rewrite
it as −2 ⁄ *b*^{4}.