t=time
d=st
r=train speed
p=plane speed
160=rt
720=pt
speed of plan is 20kmph less than 5 times speed of train
p=5r-20
we notice that 160 times 4.5=720
times first equaton by 4.5
720=4.5rt
720=pt
set equal
4.5rt=pt
divide both sides by t
4.5r=p
sub p=5r-20 for p
4.5r=5r-20
minus 4.5r from both sides
0=0.5r-20
add 20 to both sides
20=0.5r
times 2 both sides
40=r
sub back
p=5r-20
p=5(40)-20
p=200-20
p=180
plane is 180kmph
train is 40kmph
