Question 534386
Let {{{t}}} = the time for each
Let {{{s}}} = the speed of the plane
Car:
(1) {{{ 125 = ( s - 315 )*t }}}
Plane:
(2) {{{ 1515 = s*t }}}
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(2) {{{ t = 1515/s }}}
Substitute (2) into (1)
(1) {{{ 125 = ( s - 315 )*(1515/s) }}}
(1) {{{ 125 = 1515 - 477225/s }}}
(1) {{{ 125s = 1515s - 477225 }}}
(1) {{{ 1390s = 477225 }}}
(1) {{{ s = 343.327 }}} mi/hr
{{{ s - 315 = 343.327 - 315 }}}
{{{ s - 315 = 28.327 }}} mi/hr
The speed of the car is 28.327 mi/hr
The speed of the plane is 343.327 mi/hr 
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check:
(2) {{{ t = 1515/343.327 }}}
(2) {{{ t = 4.413 }}} hrs
and
(1) {{{ 125 = ( 343.327 - 315 )*4.413 }}}
(1) {{{ 125 = 28.327*4.413 }}}
(1) {{{ 125 = 125.007 }}}
Seems close enough