So far, we know that \( s=12 \) is part of the solution. Use the second equation to find the value of \( f \). \[ \begin{array}{l}0.75 f+0.5 s=9 \\ f=16-s\end{array} \] \[ \begin{array}{l}s=12 \\ f=16-s \\ f=\square\end{array} \]

First, let's substitute the value of \( s \) into the second equation. Since \( s = 12 \), we have: \[ f = 16 - s = 16 - 12 = 4. \] So, \( f = 4 \). Now, to ensure our solution makes sense, we can substitute \( s = 12 \) and \( f = 4 \) into the first equation to double-check the calculations: \[ 0.75 f + 0.5 s = 9 \] \[ 0.75 \cdot 4 + 0.5 \cdot 12 = 3 + 6 = 9. \] This confirms that the values we found are correct! Therefore, the value of \( f \) is \( \boxed{4} \).