The production function is $f(x)=20 x-x^{2}$ and the price of output is normalized to $1 .$ Let $w$ be the price of the $x$ -input. We must have $x \geq 0$
(a) What is the first-order condition for profit maximization if $x>0 ?$
(b) For what values of $w$ will the optimal $x$ be zero?
(c) For what values of $w$ will the optimal $x$ be $10 ?$
(d) What is the factor demand function?
(e) What is the profit function?
(f) What is the derivative of the profit function with respect to $w ?$