## **Core Concept**
The "rule of nine" is a method used to estimate the size of a burn injury, particularly in adults. It divides the body into sections, each representing 9% of the body's surface area. This rule helps in assessing the severity of burns and planning treatment.

## **Why the Correct Answer is Right**
According to the rule of nine, each upper limb represents 9% of the body surface area, and each lower limb represents 18%. If both upper limbs and both lower limbs are involved, the total percentage of burns would be 9% (for both upper limbs) + 18% (for both lower limbs) = 54%. Therefore, the correct calculation for the percentage of burns if both the upper limbs and lower limbs are involved is 54%.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately reflect the calculation based on the rule of nine for the described scenario.
- **Option B:** This option suggests 45%, which is incorrect because it underestimates the total body surface area affected by burns in this scenario.
- **Option D:** This option suggests 81%, which overestimates the total body surface area affected.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the "rule of nine" is specifically designed for adults. In children, the proportion of body surface area changes with age, and the Lund-Browder chart is often used instead for a more accurate estimation.

## **Correct Answer:** . 54%