1. **State the problem:** Calculate $-\frac{3}{7} \div -\frac{18}{35}$.\n\n2. **Recall division of fractions rule:** Dividing by a fraction is the same as multiplying by its reciprocal. So,\n$$-\frac{3}{7} \div -\frac{18}{35} = -\frac{3}{7} \times -\frac{35}{18}.$$\n\n3. **Multiply numerators and denominators:**\n$$\frac{-3 \times -35}{7 \times 18} = \frac{105}{126}.$$\n\n4. **Simplify the fraction:** Both numerator and denominator have a common factor of 21, so\n$$\frac{105 \div 21}{126 \div 21} = \frac{5}{6}.$$\n\n5. **Interpret signs:** Negative divided by negative gives a positive result, which matches our positive simplified fraction.\n\n**Final answer:** $$\frac{5}{6}.$$