1. **State the problem:** We need to find the total number of new cells created in 120 days if the body produces $3.3 \times 10^9$ new cells every day. 2. **Formula used:** Total cells = (cells per day) $\times$ (number of days) 3. **Apply the formula:** $$\text{Total cells} = 3.3 \times 10^9 \times 120$$ 4. **Simplify the multiplication:** $$3.3 \times 120 = 396$$ 5. **Rewrite the total cells:** $$396 \times 10^9$$ 6. **Express in scientific notation:** Move the decimal point in 396 two places to the left to get 3.96, which means: $$396 \times 10^9 = 3.96 \times 10^2 \times 10^9 = 3.96 \times 10^{11}$$ 7. **Final answer:** The number of new cells created in 120 days is $$\boxed{3.96 \times 10^{11}}$$