(a) We use the formula,
[tex]Distance = speed \times time[/tex]
The total distance covered by auto,
[tex]= 25 \ km/h \times ( 4.0 \ minutes \times \frac{1 \ h}{60 \ minutes } ) + 50 \ km/h \times ( 8.0 \ minutes \times \frac{1 \ h}{60 \ minutes }) + 20 \ km/h \times ( 2.0 \ minutes \times \frac{1 \ h}{60 \ minutes } ) \\\\ = 9.1 \ km[/tex]
(b)
Average speed = total distance / total time
Total time = 4/60 + 8 /60 + 2/60 = 14 /60
Thus, average speed
[tex]= \frac{9.1}{\frac{14}{60} } =39 \ km/ h[/tex]
Average speed in m/s,
[tex]39 \ km/ h = \frac{39 \times 10^3 \ m}{60 \times 60 s} = 10. 83 \ m/s[/tex]
