Correct Answer - Option 3 : 26.6 kmph

**Given:**

Average of speed during uphill (S_{1}) = 24 kmph

Average of speed during down (S_{2}) = 30 kmph

**Formula used:**

Average speed = (2 × S1 × S2)/(S1 + S2)

**Calculation:**

Average speed = (2 × 24 × 30)/(24 + 30)

⇒ 1440/54

⇒ 26.66 kmph

**Hence, The average speed of the entire journey is 26.66 kmph.**