Length of the train = 400 m
Car overtakes train in 8 secs

Relative speed = $$\frac{400}{8}=50ms^{-1}$$
speed of train = 36kmph converting it to m/s
$$\frac{\left(36\cdot1000\right)}{60\cdot60}=\ 10ms^{-1}$$
$$Speed\ of\ car\ =\ Relative\ speed\ +speed\ of\ train\ =50+10=60\ \frac{m}{s}$$
The car crosses another goods train B travelling in opposite directions this time around.
Speed of time B = 54km/hr
converting it to m/s
$$\frac{\left(54\cdot1000\right)}{60\cdot60}=15ms^{-1}$$
Relative speed= Speed of car +speed of train B
= 60+15 = 75m/s
Length of train B = Relative speed * time taken = 75 *4 =300m
For the two trains given that they are travelling in opposite directions, their relative speed will be
Speed of train A + speed of train B 10 + 15 = 25 m/s
Distance = Length of the two trains = 400+300 = 700m
Time taken to cross the slower train = Distance / Relative speed
$$\frac{700}{25ms^{-1}}$$
$$=28\sec$$

$$Ans\ is\ Option\ A$$