1. **State the problem:** Tessa first added 0.6 grams of salt to the soup, then added 0.9 grams more. We need to find the total amount of salt added. 2. **Formula used:** To find the total salt, we add the amounts together: $$\text{Total salt} = \text{First amount} + \text{Second amount}$$ 3. **Substitute the values:** $$\text{Total salt} = 0.6 + 0.9$$ 4. **Calculate the sum:** $$0.6 + 0.9 = 1.5$$ 5. **Answer:** Tessa put a total of 1.5 grams of salt into the soup.