To find the total mass of the 28 boxes of cereal, you would use the equation:
\[ 28 \times 375 = m \]
Now, let's calculate the total mass:
\[ 28 \times 375 = 10,500 \text{ grams} \]
Therefore, the correct response is:
\[ 28 \times 375 = m; , m = 10,500 \text{ grams} \]