Consider that the average speed is given by:
[tex]v_{\text{avg}}=\frac{s}{t}[/tex]where,
s: distance traveled = 55 km
t: time interval = 3.89 s
Replace the previous values of the parameters into the formula for v_avg:
[tex]v_{\text{avg}}=\frac{55\operatorname{km}}{3.89s}\approx14.14\frac{\operatorname{km}}{s}[/tex]Hence, the average speed is approximately 14.14 km/s