The problem asks to find the expression that is equivalent to $3(7a + 4)$.

1. Problem Description

The problem asks to find the expression that is equivalent to $3(7a + 4)$.

2. Solution Steps

To find the equivalent expression, we need to distribute the $3$ to both terms inside the parentheses:

$3(7a + 4) = 3 * 7a + 3 * 4$

$3 * 7a = 21a$

$3 * 4 = 12$

So, $3(7a + 4) = 21a + 12$.

3. Final Answer

$21a + 12$