Option 2 : 90 km/hr

**Given:**

Speed of the train in the first case = 56 km/hr

Time taken by the train in the first case = 45 minutes = 3/4 hr

Time taken by the train to cover the same distance in the second case = (45 - 17) = 28 min = 7/15 hrs

**Formula Used:**

D = S × T,

where, D = Distance, S = Speed and T = Time

**Calculation:**

Let the speed and time of the train in the first case be S1 and T1 respectively.

Similarly, let the speed and time of the train in the second case be S2 and T2 respectively.

According to the question,

T_{2} = T_{1} - 17

⇒ T_{2} = 45 - 17

⇒ T_{2} = 28 min

Now, The distance travelled by the train in both cases is the same.

So,

S_{1} × T_{1} = S_{2} × T_{2}

⇒ 56 × (3/4) = S_{2} × {(45 - 17)/60}

⇒ 14 × 3 = S_{2} × (28/60)

⇒ 14 × 3 = S_{2} × (7/15)

⇒ S_{2} = (42 × 15)/7

⇒ S_{2} = 6 × 15

⇒ S_{2} = 90 km/hr

**∴ The speed at which the train must run to reduce the time of journey by 17 minutes is 90 km/hr.**