\(\left\{{}\begin{matrix}v=\dfrac{s}{t}=\dfrac{120}{30}=4\left(\dfrac{m}{s}\right)\\v'=\dfrac{s'}{t'}=\dfrac{60}{24}=2,5\left(\dfrac{m}{s}\right)\\v_{tb}=\dfrac{s+s'}{t+t'}=\dfrac{120+60}{30+24}=\dfrac{10}{3}\left(\dfrac{m}{s}\right)\end{matrix}\right.\)