Option 3 : 180

**Calculation**:

Given,

The speed of Pradeep = 50 km/hr

The speed of Suresh = 60 km/hr

The speed of Subodh = 75 km/hr

Now, if Suresh started 90 minutes after Pradeep i.e, in 90 minutes Pradeep will travel at a distance of 75km.

By using the relative velocity concept,

Relative velocity = 75/time

⇒ 10 = 75/time

⇒ Time = 7.5 hours

So Suresh will catch Pradeep after 7.5 hours i.e. at a distance of 450km.

Now calculate how long Subodh will cover a distance of 450 km.

⇒ Time is taken by Subodh = 450/75

⇒ Time is taken by Subodh = 6 hours.

Now calculate the total time taken by Pradeep to cover 450 km.

⇒ Time is taken by Pradeep = 450/50

⇒ Time is taken by Pradeep = 9 hours.

To calculate how many minutes after Pradeep did Subodh start from the office subtract Time is taken by Subodh from time is taken by Pradeep.

⇒ Time is taken by Pradeep - Time is taken by Subodh = 9 - 6 = 3 hours = 180 minutes.

Hence option 3 is correct.

__Additional Information__

Distance is given by the formula Distance = Speed × Time.

When two bodies move in the same direction then the Relative Speed = Difference of Speeds i.e Body A moving with a speed of X km/hr and Body B moving with a speed of Y km/hr and they are moving in the same direction, then the **Relative speed = (X - Y) km/hr.**