1. We are asked to calculate two expressions: (a) $-3.5 \times -4$ and (b) $0.1 \div 0.4$.\n\n2. For part (a), multiplying two negative numbers results in a positive number.\n\n$$-3.5 \times -4 = 14$$\nThis is because the negatives cancel out and $3.5 \times 4 = 14$.\n\n3. For part (b), to divide decimals, you can convert the division into a fraction or perform decimal division:\n\n$$0.1 \div 0.4 = \frac{0.1}{0.4} = \frac{1}{10} \div \frac{4}{10} = \frac{1}{10} \times \frac{10}{4} = \frac{1}{4} = 0.25$$\n\nThus, $0.1 \div 0.4 = 0.25$.\n\nFinal answers:\n\n(a) 14\n(b) 0.25