Question 947551
You can just add the speeds to get the distance
and time elapsed between them
Let {{{ t }}} = time in hrs
{{{ 21 = ( 75 + 65 )*t }}}
{{{ 21 = 140t }}}
{{{ t = 3/20 }}}
Convert to minutes
{{{ ( 3/20 )*60 = 9 }}}
At 1:09, they will be 21 km apart