Question 1151746
Let {{{ d }}} = the distance he traveled 
for the first 40 min
{{{ 84 - d }}} = distance he traveled for the 
remaining time
Let {{{ s }}} = his speed for first 40 min
{{{ (2/3)*s }}} = his speed for remaining time
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(1) {{{ d = s*( 40/60 ) }}}
(2) {{{ 84 - d = ( (2/3)*s )*( 2 - (2/3) ) }}}
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(1) {{{ d = (2/3)*s }}}
and
(2) {{{ 84 - d = ( 4/3 )*( 2/3 )*s }}}
(2) {{{ 84 - d = ( 8/9 )*s }}}
(2) {{{ 84 - ( 6/9 )*s = ( 8/9 )*s }}}
(2) {{{ (14/9)*s = 84 }}}
(2) {{{ s = 54 }}} 
His original speed was 54 mi/hr
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check:
{{{ d = (2/3)*s }}}
{{{ d = (2/3)*54 }}}
{{{ d = 36 }}} mi
and
(2) {{{ 84 - d = ( 8/9 )*s }}}
(2) {{{ 84 - d = 48 }}}
(2) {{{ d = 36 }}} mi
OK