Question 1056202
Let {{{ d }}} = distance from point of no return to NYC
{{{ 3458 - d }}} = distance from point of no return to London
Let {{{ t }}} = time in hrs to fly from point of no return
back to NYC and also the time in hrs to London
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Equation for point of no return back to NYC
(1) {{{ d = ( 900 - 70 )*t }}}
Equation for point of no return to London 
(2) {{{ 3458 - d = ( 900 + 70 )*t }}}
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Note that you have to keep track of the wind direction.
Substitute (1) into (2)
(2) {{{ 3458 - ( 900 - 70 )*t = ( 900 + 70 )*t }}}
(2) {{{ 3458 - 900t + 70t = 900t + 70t }}}
(2) {{{ 1800t = 3458 }}}
(2) {{{ t = 1.921 }}} hrs
This is 1 hr 55 min 16 sec
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Check:
(1) {{{ d = ( 900 - 70 )*t }}}
(1) {{{ d = 830t }}}
(1) {{{ d = 830*1.921 }}}
(1) {{{ d = 1594.43 }}}
and
(2) {{{ 3458 - d = ( 900 + 70 )*t }}}
(2) {{{ 3458 - d = 970t }}}
(2) {{{ d = 3458 - 970t }}}
(2) {{{ d = 3458 - 970*1.921 }}}
(2) {{{ d = 3458 - 1863.37 }}}
(2) {{{ d = 1594.63 }}}
Close enough, I think -OK