Explanation:

Let's evaluate each option to find which interchange makes the original equation correct:

- Original Equation: 3 ÷ 6 - 2 + 8 × 4 = 18

1. Interchange ÷ and -:

- New Equation: 3 - 6 ÷ 2 + 8 × 4

- Solves to: (3 - 3 + 32) = 32. Not 18, so incorrect.

2. Interchange + and ÷:

- New Equation: 3 + 6 - 2 ÷ 8 × 4

- Solves to: (3 + 6 - 1) = 8. Not 18, so incorrect.

3. Interchange ÷ and ×:

- New Equation: 3 × 6 - 2 + 8 ÷ 4

- Solves to: (18 - 2 + 2) = 18. Correct!

4. Interchange + and -:

- New Equation: 3 ÷ 6 + 2 - 8 × 4

- Solves to: (0.5 + 2 - 32) = -29.5. Not 18, so incorrect.

Correct Answer: Option 3 — Interchange ÷ and ×.