(d) 105 metres
Let the length of train be l metres and its speed be x m/s.
Then, \(\frac{l}{x} = 1.5 ⇒l=1.5x\) .....(i)
and \(\frac{l}{(x-10)}=1.75 ⇒ l = 1.75(x-10)\)
⇒ l = 1.75x – 17.5 ...(ii)
From (i) and (ii),
1.5x = 1.75x – 17.5 ⇒ 0.25x = 17.5
⇒ x = \(\frac{17.5}{0.25}\) = 70 m/s
∴ Length of the train = (1.5 × 70) metres = 105 metres.