An endurance runner should eat 1.2 grams of carbohydrates per kilogram (kg) of body weight each hour when running for 4 hours. How many grams of carbohydrates should a runner weighing 78 kg eat after the first hour of running?

Solution:
1. Given:
* The runner's weight: 78 \, \text{kg}
* Carbohydrate intake required per kilogram per hour: 1.2 \, \text{grams/kg/hour}

2. Calculate the total amount of carbohydrates needed for one hour:
* Carbohydrate intake needed per hour: 78 \, \text{kg} \times 1.2 \, \text{grams/kg/hour} = 93.6 \, \text{grams}

Therefore, the amount of carbohydrates needed by the runner after the first hour of running is:
93.6 \, \text{grams}

3. Final answer:
The runner should eat 93.6 \, \text{grams} of carbohydrates after the first hour of running.