The (15x^-6) or (15/x^6) expression is equivalent to (3x^-4)(5x^-2) based on the rule of the exponential number or the rule of the exponential of a variable. The rule of the exponential number or the rule of the exponential of a variable states the 1/x expression is the same as x^-1 and x^y * x^z is the same as x^(y+z). Therefore, we can change the expression to become (3*5)/(x^4*x^2) resulting in the answer of (15/x^6) = (15x^-6).