Correct Answer - Option 1 : 8 km/h

**Given:**

Distance travelled = 120 km

Increase in speed = 4 km/h

Difference in time taken = 5 hrs

**Formula used:**

Time taken = Distance/speed

**Calculation:**

Let the initial speed = x km/h

∵ Initial time taken - New time taken = 5 hrs

⇒ 120/x - 120/(x + 4) = 5

⇒ 120x + 480 - 120x = 5x(x + 4)

⇒ 480 = 5x^{2} + 20x

⇒ x2 + 4x - 96 = 0

⇒ x2 + 12x - 8x - 96 = 0

⇒ x(x + 12) - 8(x + 12) = 0

⇒ (x - 8)(x + 12) = 0

∴ x - 8 = 0

⇒ x = 8 km/h

x + 12 = 0

⇒ x = (-12) km/h Not possible

∴ Actual speed = 8 km/h