The degree of longitude through which the Earth spins within 3hours is

Analyze the question: We need the number of degrees of longitude the Earth rotates through in 3 hours.

Concept: The Earth rotates 360° in 24 hours, so it turns through:

360° ÷ 24 hours = 15° per hour

(This is also why every 15° of longitude equals 1 hour of time difference, or 1° equals 4 minutes.)

Solution:

Degrees in 3 hours = 15° × 3 = 45°

Checking the options:

• A. 15° is for 1 hour
• B. 30° is for 2 hours
• C. 45° is for 3 hours ✔
• D. 60° is for 4 hours

Tip: Memorize "15° = 1 hour". For any such question, just multiply the number of hours by 15. For example, 5 hours gives 75°, and 6 hours gives 90°. This also helps you with time-zone questions, where you divide the longitude difference by 15 to get the time difference.