How much food to give 6 mo old & every 4 hours?

This is a question to be answered by your Doctor.

Generally, it will depend on baby's weight, are they taking in a fair amount of solid foods yet or just breastmilk or formula? As JudyKayTee said, check with your doctor if you are unsure from the cues baby is giving you. Baby's doctor may have a specific reason they want you to offer more or less.

Every four hours can be fine as long as they are getting what they need in that time. Rough guide is about 24-32 ounces a day... again it will depend on how much solid food they may be having. Their milk should still be the main source of nutrition, so they should be having more milk than solids for awhile longer yet. This will gradually change as the first year progresses.