Question 1136344
Add their rates of travel
Let {{{ t }}} = time in hrs
{{{ 680 = ( 90 + 80 )*t }}}
{{{ 680 = 170t }}}
{{{ t = 4 }}}
In 4 hrs they are 680 km apart
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check:
{{{ d[1] = 90*4 }}}
{{{ d[1] = 360 }}}
and
{{{ d[2] = 80*4 }}}
{{{ d[2] = 320 }}}
and
{{{ d[1] + d[2] = 360 + 320 }}}
{{{ d[1] + d[2] = 680 }}}
OK