Answer
$Average$ $speed =6.0m/s$
Work Step by Step
$1.2 min=(1.2min)(\frac{60s}{1min})=72s$
$Average$ $speed = \frac{distance}{elapsed time}$. Now, rearrange for the distance:
$Distance=(average$ $speed)(elapsed$ $time)$. So:
$Distance_{1}=(0.060m/s)(72s)=4.32m$
$Distance_{2}=(12m/s)(72s)=864m$
$Total$ $distance=4.32m+864m=868.32m$
$Total$ $elapsed$ $time=72s+72s=144s$
$Average$ $speed =\frac{86832m}{144s}=6.0m/s$
