Question 1071216
<pre>
              SPEED       TIME      DISTANCE
SKATE          r           t          12
BIKE          2r          t-2         12
</pre>


{{{system(rt=12,(2r)(t-2)=12)}}}


{{{2rt-4r=12}}}
{{{2*12-4r=12}}}
{{{2*3-r=3}}}
{{{-r=3-6}}}
{{{highlight(r=3)}}}----------speed on skateboard


{{{rt=12}}}
{{{t=12/r}}}
{{{t=12/3}}}
{{{highlight(t=4)}}}---------time, hours, on skateboard


{{{t-2=highlight(2)}}}-------time going back by bicycle