First, the nurse determines how many ounces the baby eats in a day. Eating every 3 hours means the baby takes 8 bottles in a day.

$$ { 3 \text{ ounces} \over \text{feeding}} * { 8 \text{ feedings} \over 1 \text{ day}} = 24 \text{ounces/day} $$

Then, the nurse determines how many total kilocalories are ingested by multiplying the total volumes by the number of kilocalories in breast milk: 20kcal/oz.

$$ { 24 \text{ ounces} \over \text{day}} * { 20 kcal \over 1 \text{ ounce}} = 480 \text{kcal/day} $$

Lastly, the nurse divides the result by the infant’s weight to determine the patient’s nutritional intake.

$$ {480 kcal \over \text{day}} * {1 \over 4.1 kg} $$