Given $f(x, y)=80 x+50 y-5 x^{2}-4 y^{2}-x y$ Evaluate $f(1,9)$ \[ f(1,9)= \]

Step 1 ：Given the function \(f(x, y)=80 x+50 y-5 x^{2}-4 y^{2}-x y\)

Step 2 ：We need to evaluate \(f(1,9)\)

Step 3 ：Substitute \(x=1\) and \(y=9\) into the function

Step 4 ：After simplifying the expression, we get \(f(1,9)=192\)

Step 5 ：Final Answer: \(\boxed{192}\)