Question 569986
Let {{{ s }}} = speed of plane in still air
Let {{{ w }}} = wind speed
{{{ s + w }}} = speed of plane with tail wind
{{{ s - w }}} = speed of plane against the wind
{{{ 45 }}} min = {{{ 3/4 }}} hr
{{{ 48 }}} min = {{{ 4/5 }}} hr
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given:
(1) {{{ s + w = 240/( 3/4) }}}
(2) {{{ s - w = 240/( 4/5 ) }}}
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(1) {{{ s + w = (4/3)*240 }}}
(2) {{{ s - w = (5/4)*240 }}}
Add the equations
{{{ 2s = 240*( 4/3 + 5/4 ) }}}
{{{ s = 120*( 4/3 + 5/4 ) }}}
{{{ s = 120*( 16/12 + 15/12 ) }}}
{{{ s = 10*( 16 + 15 ) }}}
{{{ s = 310 }}}
and
(1) {{{ s + w = (4/3)*240 }}}
(1) {{{ 310 + w = (4/3)*240 }}}
(1) {{{ w = 320 - 310 }}}
(1) {{{ w = 10 }}} 
Air speed is 310 km/hr
wind speed is 10 km/hr
check:
(1) {{{ s + w = 240/( 3/4) }}}
(1) {{{ 310 + 10 = 240/( 3/4) }}}
(1) {{{ 320 = (4/3)*240 }}}
(1) {{{ 960 = 4*240 }}}
(1) {{{ 960 = 960 }}}
and
(2) {{{ s - w = 240/( 4/5 ) }}}
(2) {{{ 310 - 10 = 240/( 4/5 ) }}}
(2) {{{ 300 = (5/4)*240 }}}
(2) {{{ 1200 = 1200 }}}
OK