1. Problem statement: Evaluate $3.4 - (-6.9) \times 2.4$. 2. Rule and formula: Use the order of operations, do multiplication before subtraction. 3. General formula useful here: $$a - (-b) \times c = a + b \times c$$ 4. Explanation: Because subtracting a negative product is the same as adding the positive value of that product. 5. Compute the product step by step: First compute $(-6.9) \times 2.4$. 6. Multiply absolute values: $6.9 \times 2.4 = \frac{69}{10} \times \frac{24}{10} = \frac{1656}{100} = 16.56$. 7. Include the sign: $(-6.9) \times 2.4 = -16.56$. 8. Now perform the subtraction: $3.4 - (-16.56) = 3.4 + 16.56$. 9. Add to get the final result: $3.4 + 16.56 = 19.96$. 10. Final answer: $19.96$.