A linear programming model has been formulated for two products, X and Y. The objective fu

nction 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 2 kg of material Z and each unit of Y uses 3 kg 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 $2·80 per kg. If an extra 20 kg of material Z becomes available at $2 per kg, what will the maximum increase in contribution be？

A.Increase of $96

B.Increase of $56

C.Increase of $16

D.No change