A linear programming model has been formulated for two products, $x$ and $Y.$ the objective function is depicted by the formula $C=5x+6Y,$ where $C=$ Contribution, $x=$ the number of product $x$ to be produced and $Y=$ the number of product $Y$ to be produced.

Each unit of $x$ uses $2kg$ of material $Z$ and each unit of $Y$ uses $3kg$ of Material $Z.$ The standard cost of material $Z$ is $2$ per $kg.$

The shadow price for material $Z$ has been worked out and found to be $2\mathrm{.}80$perkg.

If an extra $20kg$ of material $Z$ becomes available at $2$ per $kg.$

What will the maximum increase in contribution be$?$

A$.$ Increase of $96$

B$.$ Increase of $16$

C$.$ Increase of $56$

D$.$ No change