Let's solve the equation step by step.
You have the equations:
- \( 0.75f + 0.5s = 9 \)
- \( f = 16 - s \)
Substituting the second equation into the first equation:
\[ 0.75(16 - s) + 0.5s = 9 \]
Now distribute \( 0.75 \):
\[ 0.75 \times 16 - 0.75s + 0.5s = 9 \]
Calculating \( 0.75 \times 16 \):
\[ 12 - 0.75s + 0.5s = 9 \]
Combine like terms:
\[ 12 - 0.25s = 9 \]
Now, isolate \( -0.25s \) by subtracting 12 from both sides:
\[ -0.25s = 9 - 12 \]
\[ -0.25s = -3 \]
Now, divide by -0.25 to find \( s \):
\[ s = \frac{-3}{-0.25} \]
Calculating the division:
\[ s = 12 \]
Thus, the value of \( s \) is \( \boxed{12} \).