To analyze the expression \( 21 + 9 \) in relation to the model, let's break it down.
The model shows 3 rows of 7 squares:
- This represents \( 3 \times 7 = 21 \).
And it also shows 3 rows of 3 squares:
- This represents \( 3 \times 3 = 9 \).
So we have:
- The total is \( 21 + 9 \).
Now let's look through the options provided to find an equivalent expression.
A. \( 3(7 + 3) \): This means \( 3 \times (7 + 3) = 3 \times 10 = 30 \). This is not equivalent.
B. \( 3(7) + 3 \): This simplifies to \( 21 + 3 = 24 \). This is not equivalent.
C. \( 3 + 7 + 3 \): This is \( 3 + 7 + 3 = 13 \). This is not equivalent.
D. \( 7(3 + 3) \): This means \( 7 \times (3 + 3) = 7 \times 6 = 42 \). This is not equivalent.
None of the expressions provided, in their current forms, are equivalent to the given sum \( 21 + 9 \) which equals \( 30 \).
It appears that based on the given options, none correctly match up to \( 21 + 9 \) in their currently provided forms that can be simplified or calculated.
Therefore, it seems that there may be a misunderstanding with the options or the question prompt itself, as they do not represent an equivalent statement for \( 21 + 9 \).
If the goal was simply to calculate, then \( 21 + 9 = 30 \) is the sum, but it doesn’t match any of the expressions listed.