Step 1: Match the expression to the standard binomial square formula.
The formula is $(x - y)^{2} = x^{2} - 2xy + y^{2}$.
Given terms: $16a^{2} - 12a$.
Let $x^{2} = 16a^{2}$, which means $x = 4a$.
Step 2: Solve for $y$.
The middle term is $-2xy = -12a$.
Substitute $x = 4a$: $-2(4a)y = -12a \Rightarrow -8ay = -12a \Rightarrow y = \frac{12}{8} = \frac{3}{2}$.
Step 3: Find the missing term $y^{2}$.
To complete the square, we must add $y^{2}$.
$y^{2} = (\frac{3}{2})^{2} = \frac{9}{4}$.