To evaluate $(6.4 \times 10^6) + (3.1 \times 10^5)$ and express the result in scientific notation, follow these steps:

Step 1: Rewrite the terms with the same power of 10.

The powers of 10 are $10^6$ and $10^5$. To combine the terms, rewrite $3.1 \times 10^5$ with the same power as $6.4 \times 10^6$.

$3.1 \times 10^5 = 0.31 \times 10^6$

Now, the expression becomes: $(6.4 \times 10^6) + (0.31 \times 10^6)$

Step 2: Factor out $10^6$.

Combine the coefficients: $(6.4 + 0.31) \times 10^6 = 6.71 \times 10^6$

Step 3: Express the result in scientific notation.

The result is: $6.71 \times 10^6$

Final Answer:

$\boxed{6.71 \times 10^6}$

Would you like more details or have any questions? Here are some related questions to explore further:

1. How do you convert numbers to scientific notation?
2. What are the rules for adding and subtracting numbers in scientific notation?
3. Can you apply the same method to subtract $(8.2 \times 10^7) - (5.4 \times 10^6)$?
4. How do different powers of 10 affect addition in scientific notation?
5. What are practical examples of using scientific notation in real life?

Tip: When adding numbers in scientific notation, always align the exponents before combining the coefficients.