Question 1157496
Let {{{ t }}} = the time in hrs for the trip without the wind
Let {{{ d }}} = the distance to their destination
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Without the wind:
(1) {{{ d = 140t }}}
With the tailwind:
(2) {{{ d = ( 140 + 28 )*( t - 15/60 ) }}}
(2) {{{ d = 168*( t - 1/4 ) }}}
(2) {{{ d = 168t - 42 }}}
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Plug (1) into (2)
(2) {{{ 140t = 168t - 42 }}}
(2) {{{ 28t = 42 }}}
(2) {{{ t = 1.5 }}}
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With the wind, the time is: 
{{{ t - .25 = 1.5 - .25 }}}
{{{ t - .25 = 1.25 }}}
With the tailwind, the flight will take 1 hr 15 min
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check:
(1) {{{ d = 140t }}}
(1) {{{ d = 140*1.5 }}}
(1) {{{ d = 210 }}} mi
and
(2) {{{ d = 168*( t - 1/4 ) }}}
(2) {{{ d = 168*( 1.5 - .25 ) }}}
(2) {{{ d = 168*1.25 }}}
(2) {{{ d = 210 }}} mi
OK