A ball is thrown vertically upwards at $19\mathrm{.}6$ m$/$s$.$ For its complete trip $($up and back down to the starting position$),$ its average speed is:A$)9\mathrm{.}80$ m$/$s$.$B$)19\mathrm{.}6$ m$/$s$.$C$)$ not given.D$)4\mathrm{.}90$ m$/$s$.$