Answer:
(i) Relative velocity of B w.r.t A= Sum of speeds of trains
=54+90
=144kmph
(ii)Relative velocity of B w.r.t Ground(G)=v
B/G
=−90kmph
v
G
=0
Relative velocity of ground(G) w.r.t B =v
G/B
=v
G
−v
B/G
v
G/B
=0−(−90)
v
G/B
=90kmph