1. **State the problem:** Calculate the sum of 3455 and 3425. 2. **Formula used:** Addition of two numbers is done by adding their digits starting from the rightmost digit. 3. **Step-by-step addition:** $$3455 + 3425$$ Add the units digits: $5 + 5 = 10$, write 0 and carry 1. Add the tens digits plus carry: $5 + 2 + 1 = 8$. Add the hundreds digits: $4 + 4 = 8$. Add the thousands digits: $3 + 3 = 6$. 4. **Final result:** $$3455 + 3425 = 6880$$ So, the sum of 3455 and 3425 is **6880**.