53 kilometers in 4 hours.
then
99 kilometers in 4 hours again.
it travelled a total of 53 + 99 kilometers, and it did it in 4+4 hours, so on average, it travelled at [tex] \bf \cfrac{53+99}{4+4}\implies \cfrac{152}{8}\implies 19~\frac{km s}{hr} [/tex]
