In general if you have a negative exponent that means "make it a fraction where 1 divided by whatever the number was except with a positive exponent."
Why? When you multiply you add exponents like in (2^4)(2^6) = 2^(4+6) = 2^10. Some number x is the same as x^1, so consider how x(1/x) = 1 and x^1(x^-1) = x^0 = 1 so x(1/x) = x(x^-1) which means (1/x) = x^-1