a1=_(3(_)+4)=_

To solve the equation a1 = 3(a + 4), we need to distribute the 3 to both terms inside the parentheses:

a1 = 3a + 12

Since we want to solve for a, we need to isolate the variable on one side of the equation. We can do this by subtracting 12 from both sides:

a1 - 12 = 3a

Next, we can rearrange the equation by bringing the term with the variable to the left side:

3a = a1 - 12

Finally, we can divide both sides of the equation by 3 to solve for a:

a = \frac{a1 - 12}{3}

Answer: \boxed{a = \frac{a1 - 12}{3}}