Question 420155
Write an equation for both trains
Let {{{s}}} = speed of freight train
passenger train 
(1) {{{d+ 30 = 2s*(3/4)}}} 
freight train
(2) {{{d = s*(3/4)}}}
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Substitute (2) into (1)
(1) {{{(3/4)*s  + 30 = (3/4)*2s}}}
(1) {{{3s + 120 = 6s}}}
(1) {{{3s = 120}}}
(1) {{{s = 40}}}
and
{{{2s = 80}}}
the speed of the passenger train is 80 mi/hr
the speed of the freight train is 40 mi/hr
check:
(1) {{{d+ 30 = 80*(3/4)}}} 
(1) {{{d = 60 - 30}}}
{{{d = 30}}} mi
and
(2) {{{d = 40*(3/4)}}}
{{{d = 30}}} mi
OK