A shelf contains 28 boxes of cereal. Each box has a mass of 375 grams.

To find the total mass of the boxes of cereal, you can use the equation:

\[ 28 \times 375 = m \]

Now, let's calculate the total mass, \( m \):

\[
m = 28 \times 375
\]

Let's do the multiplication:

\[
28 \times 375 = 10,500 \text{ grams}
\]

So, the correct equation is \( 28 \times 375 = m \) and the total mass, \( m \), is **10,500 grams**.

The correct option is:
**28 x 375 = m; m = 10,500 grams.**