1. **State the problem:** We need to find how many milligrams of vitamin C are in 1 orange, given that 1 orange has about 75% of the recommended daily allowance (RDA) of 45 mg. 2. **Formula used:** To find the amount corresponding to a percentage of a total, use the formula: $$\text{Amount} = \text{Percentage} \times \text{Total}$$ where Percentage is expressed as a decimal. 3. **Convert percentage to decimal:** $$75\% = \frac{75}{100} = 0.75$$ 4. **Calculate the amount of vitamin C in 1 orange:** $$\text{Amount} = 0.75 \times 45$$ 5. **Multiply:** $$0.75 \times 45 = 33.75$$ 6. **Interpretation:** 1 orange contains 33.75 milligrams of vitamin C. **Final answer:** $$\boxed{33.75 \text{ mg}}$$