Correct Answer - Option 2 : (8, 12) hours

**Given∶**

Distance = 640 km

Speed on uphill = 20 km/hr

Speed on down hill = 40 km/hr

Time = 20 hours

**Formula Used∶**

Concept of Linear Equations, Distance = Speed × Time

**Calculation∶**

Let the time takes for uphill journey = x hrs

time takes for downhill journey = y hrs

∴ x + y = 20

and 20x + 40y = 640

Solving above equations, we get

20y = 240

⇒ y = 240/20 = 12 and

x + 12 = 20

⇒ x = 20 - 12 = 8

**∴ Time taken for Uphill journey is 8 hours and for Down hill journey is12 hours.**