then -2/27 * 27/q = 54/27Q = 2/1q =2/q
is that correct
Note that
$\displaystyle 27=3^3$
so $\displaystyle
27^-1/3 = (3^3)^-1/3 $
where the exponents cancel and we are left with 1/3. There is no negative, the negative exponent simply indicates that we have 1 over the value.