When a question asks for rate of change, this means you need to differentiate the equation. First you need to put the equation into differentiable a form ie, with the no variables on the denominator: f(t) = 2/3t^-1Then you can differentiate by multiplying the coefficient by the power and then reducing the power by one: f'(t)= -2/3t^-2We can put this back to a standard form to make it easier to work with: f'(t) = -2/(3t^2)Substitute t = 6 in and we get: f-(t) = -2/(3*36) = -2/108 = -1/54