Explanation:

- We have a flag with 4 horizontal stripes.

- Each stripe can be colored using red, green, or yellow.

- No two adjacent stripes can have the same color.

- Calculate possibilities for each strip:

- The first stripe can be any of the 3 colors.

- The second stripe can be any of the 2 remaining colors not used by the first stripe.

- The third stripe can be any of the 2 colors not used by the second stripe.

- The fourth stripe can be any of the 2 colors not used by the third stripe.

- Calculation:

- 3 options for the first,

- 2 options for the second,

- 2 options for the third,

- 2 options for the fourth.

- Multiply possibilities: 3 * 2 * 2 * 2 = 24.

- ?? Correct Answer: Option 3, 24.