A School Is Trying to Determine a Nutritional Diet to Feed

A school is trying to determine a nutritional diet to feed its students.The school would like to offer some combination of milk and beans.The school's objective is to minimize cost,subject to meeting the minimum nutritional requirements of protein,calcium,and calories.The cost and nutritional content of each food,along with the minimum nutritional requirements are shown here. $$\begin{array} { | l | l | l | l | } \hline \text { Nutrient } & \begin{array} { l } \text { Kidney } \\\text { Beans }\end{array} & \text { Tofu } & \begin{array} { l } \text { Minimum Daily } \\\text { Requirement }\end{array} \\\hline \text { Cost per pound } & \$ 0.90 & \$ 1.50 & \\\hline \begin{array} { l } \text { Calcium in units per } \\\text { pound }\end{array} & 15 & 6 & 30 \\\hline \text { Protein in units per pound } & 10 & 10 & 40 \\\hline \begin{array} { l } \text { Calories in units per } \\\text { pound }\end{array} & 3 & 9 & 18 \\\hline\end{array}$$ At the optimum solution,what is the number of pounds of tofu included in the diet?

A) 1
B) 2
C) 3
D) 4