The exponents distribute over factors:
[tex] (ab)^c = a^c \times b^c [/tex]
so, you have
[tex] (3.2 \times 10^6)^{-3} = 3.2^{-3} \times (10^6)^{-3} [/tex]
Let's focus on each factor: applying the definition of negative exponents, you have
[tex] 3.2^{-3} = \cfrac{1}{3.2^3} \approx 0.03 [/tex]
While for the power of 10, you can use the following rule
[tex] (a^b)^c = a^{bc} [/tex] to write
[tex] (10^6)^{-3} = 10^{6\cdot (-3)} = 10^{-18} [/tex]
So, the expression evaluates to
[tex] 0.03\times 10^{-18} = 3\times 10^{-20} [/tex]
