The Cost Associated with Storing $x$ Units of a Certain Product Is Given by the Function

Essay

The cost associated with storing $x$ units of a certain product is given by the function $C ( x ) = 0.8 x ^ { 2 } - 12.8 x + 2600$ where $C$ is measured in of dollars and $x$ in hundreds of units.
(a) For what values of
$x$ will the cost be decreasing? increasing?
(b) What is the minimum cost?