The distince $x$ meters traveled by a vehical in time $t$ seconds after the brakes are applied is given by:$\;x=20 t-\large\frac{5}{3}$$t^{2}$. Determine the speed of the vehicle (in km/hr) at the instant the brakes are applied

Question

This is part 1st of a 2 part question, split as 2 separate questions here.