To simplify, you need to distribute the -6 out into both the 2 and the t to get:
[tex] 2^{-6} * t^{-6} [/tex]
Now, if you only want positive exponents, you need to write the expression in this form:
[tex] \frac{1}{ 2^{6}* t^{6} } [/tex]
Which would simplify to:
[tex]\frac{1}{ 64t^{6}}[/tex]
