Answer: On mange le petit déjeuner à 8H.
Explanation: 8H is 8 am. Le petit déjeuner is breakfast.
le déjeuner is lunch, eaten usually around midi whichnos noon.
le dîner is dinner, which may be eaten around 7 or 8 pm in France, but they use the 24-hour time so those would be 19H or 20H.
le goûter is "snack" or "afternoon tea" which is usually served in the late afternoon.