The amount of yeast to add to flour depends on the recipe and the desired rise and fermentation time. As a general guideline, a common ratio is to use 1 to 2 percent of the flour's weight for active dry yeast.
To calculate the amount of yeast to add to 3 kg of flour:
1 percent of 3 kg = 0.01 x 3000 g = 30 g 2 percent of 3 kg = 0.02 x 3000 g = 60 g
So, you can add between 30 grams and 60 grams of yeast to 3 kg of flour, depending on the desired rise and fermentation time. It's important to note that these are general guidelines, and for more specific recipes, it's best to refer to the instructions provided.