A firm's average cost (AC) per unit of output depends on the number of hours of skilled

A firm's average cost (AC) per unit of output depends on the number of hours of skilled

labor (S) and the number of hours of unskilled labor (U) employed in the production process. The firm's AC function is defined below. Determine the quantities of the two inputs that will result in production at the lowest possible average cost and determine the associated minimum average cost.

AC = 3S22 + 2U22 - 2SU - 2S - 6U + 20