The operating cost of a truck is `12+(x/6)` per km when the truck travels x km/hour. If the driver earns 6 Rs. per hour, what is the most economical speed to operate the truck on a 400 km road? Also due to construction, the truck can travel only between 35 and 60 km/hour?

Explanation

To solve the problem step by step, we will first define the total operating cost of the truck and then find the most economical speed for the truck to travel on a 400 km road.

### Step 1: Define the Operating Cost
The operating cost per kilometer when the truck travels at \( x \) km/hour is given by:
\[ \text{Operating Cost} = 12 + \frac{x}{6} \text{ Rs/km} \]

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