At time t t\,t seconds, where t≥0t \ge 0t≥0, a particle P P\,P has position vector r=[(t2−4t)i+3tj]\mathbf{r} = \left[(t^2 - 4t)\mathbf{i} + 3t\mathbf{j}\right]r=[(t2−4t)i+3tj] m.
Find the values of t t\,t at which the speed of P P\,P is 5 m s−1^{-1}−1.