A curve for which \(\frac{dy}{dx} = 7 - x^2 - 6x\) passes through the point \((3, -10)\).

(i) Find the equation of the curve.

(ii) Express \(7 - x^2 - 6x\) in the form \(a - (x + b)^2\), where \(a\) and \(b\) are constants.

(iii) Find the set of values of \(x\) for which the gradient of the curve is positive.