1. **State the problem:** Ris uses three-fifths of a bag of flour to make pancakes, and after that, 600g of flour is left. We need to find out how much flour she used. 2. **Set up the equation:** Let the total amount of flour in the bag be $x$ grams. 3. Since Ris uses three-fifths of the flour, the amount used is $\frac{3}{5}x$. 4. The amount left after using the flour is $x - \frac{3}{5}x = \frac{2}{5}x$. 5. We know the amount left is 600g, so: $$\frac{2}{5}x = 600$$ 6. Solve for $x$ by multiplying both sides by $\frac{5}{2}$: $$x = 600 \times \frac{5}{2} = 600 \times 2.5 = 1500$$ 7. The total flour in the bag is 1500g. 8. To find how much flour Ris used, calculate three-fifths of 1500g: $$\frac{3}{5} \times 1500 = 3 \times 300 = 900$$ **Answer:** Ris used 900 grams of flour.