A Company Is Planning Production for the Next 4 Quarters

A company is planning production for the next 4 quarters.They want to minimize the cost of production.The production cost,demand and production capacity vary from quarter to quarter.The maximum amount of inventory which can be held is 100 units and management wants to keep at least 50 units on hand.Quarterly inventory holding cost is 4% of the cost of production.There are currently 50 units in inventory.The company wants to produce at no less than one half of its maximum capacity in any quarter.
Quarter
$$\begin{array} { r r r r r } &1&2&3&4\\\hline \text { Unit Praduction Cost } & \$ 55 & \$ 50 & \$ 50 & \$ 45 \\\text { Units Demanded } & 100 & 150 & 180 & 120 \\\text { Maramum Production } & 150 & 150 & 160 & 130 \\\text { Holding cost } & \$ 2.2 & \$ 2 & \$ 2 & \$ 1.8\end{array}$$
Let ^P_i ^{= number of units produced in quarter i,i = 1,... ,4} B_i = beginning inventory for quarter i
MIN: ^{55 P}₁ ^{+ 50 P} ₂ ^{+ 50 P}₃ ^{+ 45 P}₄ ⁺
2.2 B₁ + B₂)/2 + 2 B₂ + B₃)/2 + 2 B₃ + B₄)/2 + 1.8 B₄ + B₅)/2
Subject to: ^{75 ? P}₁ ^{? 150}
75 ? P₂ ? 150
80 ? P₃ ? 160
65 ? P₄ ? 130
50 ? B₁ + P₁ ? 100 ? 100
50 ? B₂ + P₂ ? 150 ? 100
50 ? B₃ + P₃ ? 180 ? 100
50 ? B₄ + P₄ ? 120 ? 100
B₂ = B₁ + P₁ ? 100
B₃ = B₂ + P₂ ? 150
B₄ = B₃ + P₃ ? 180
B₅ = B₄ + P₄ ? 120
P_i,B_i ? 0

What formulas are required for cells D3,D6,D8,D15,D17 and D18 in the Excel spreadsheet implementation of the formulation?