To find the total mass \( m \) of the 20 boxes of cereal, you can use the equation:
\[ m = n \times b \]
where:
- \( n \) is the number of boxes (which is 20 in this case),
- \( b \) is the mass of each box (which is 375 grams).
Substituting the values:
\[ m = 20 \times 375 \]
Now, calculating that:
\[ m = 7500 \]
Thus, the total mass \( m \) in grams is 7500 grams.