A particle \(P\) is moving in a straight line such that its displacement, \(s\text{ m}\), from a fixed point \(O\) at time \(t\text{ s}\), is given by \(s=12e^{-0.5t}+4t-12\).

(i) Find the value of \(t\) when \(P\) is instantaneously at rest.

(ii) Find an expression for the acceleration of \(P\) at time \(t\text{ s}\).

(iii) Find the value of \(s\) when the acceleration of \(P\) is \(0.3\text{ m s}^{-2}\).

(iv) Explain why the acceleration of the particle will always be positive.