so a the start 180 passengers are on the train
at the first stop x get off and 24 get on or
180-x+24=204-x
at the second stop half get off and 40 get on or
204-x-([204-x]/2)+40 or
204-x-102+x/2+40
104-1/2x+40
144-1/2x
there are now 134 passengers
144-1/2x=134
subtract 134 from both sides
10-1/2x=0
add 1/2x to both sides
10=1/2x
mutliply both sides by 2/1 to make 1/2x=1/1x
20=x
20 got off at the first stop