Let's solve each of the given mathematical problems one by one:

a. Addition

1. $26,986 + 23,487 = 50,473$
2. $298,79 + 234 = 532,79$
3. $134,098 + 745,86 = 134,843.86$

b. Subtraction

1. $2,846.76 - 124,897 = -122,050.24$
2. $768.9 - 45,987 = -45,218.1$
3. $876 - 123,987 = -123,111$

c. Multiplication

1. $655.8 \times 0.65 = 426.27$
2. $98.76 \times 68 = 6,715.68$
3. $98.76 \times 9.4 = 928.944$

d. Division

1. $6,355.87 \div 32 = 198.61$
2. $879 \div 36 = 24.42$
3. $39.76 \div 5.2 = 7.65$
4. $87 \div 0.43 = 202.33$

Would you like more details or explanations for any of these steps?

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Further Questions:

1. How do you handle operations with decimal numbers in multiplication and division?
2. What is the importance of rounding in practical applications of these operations?
3. Can you describe the role of the order of operations in solving complex arithmetic problems?
4. How do negative results in subtraction and division affect subsequent calculations?
5. What are some common rounding techniques used in financial calculations?

Tip: When working with decimals in calculations, always ensure you're aligning the decimal points to avoid mistakes, especially when adding or subtracting.