The best explanation of Miriam's error is:
Miriam multiplied correctly, but her third fraction should be StartFraction 1 ounce Over 28.35 grams EndFraction.
To convert kilograms to ounces, the correct setup should account for the conversion from kilograms to grams and then from grams to ounces. Miriam mistakenly used the fraction that multiplied grams by ounces in the wrong manner. The correct conversion from grams to ounces should use the fraction \( \frac{1 \text{ ounce}}{28.35 \text{ grams}} \) to convert grams into ounces.
The proper calculation should look like this:
\[ 7 \text{ kg} \times \frac{1000 \text{ grams}}{1 \text{ kg}} \times \frac{1 \text{ ounce}}{28.35 \text{ grams}} \]
This will give her the correct number of ounces.