78.9 kg.
To convert 78,900 grams to kilograms, we can divide the number of grams by 1,000. Since 1 kilogram is equal to 1,000 grams, dividing the number of grams by 1,000 will give us the equivalent number of kilograms.
Therefore, 78,900 grams is equivalent to 78,900 / 1,000 = 78.9 kilograms.