Considering all the $4$ installations for simultaneously optimizing the entire supply chain, which installations will be theoretically merged for

calculating the optimum order quantity?

Ordering cost

K$1=3500$

Holding cost

h $1=20$

Lot size Q$1$

Ordering cost

$K2=1500$

Holding cost

h$2=50$

Lot size Q$2$

Ordering cost

K$4=200$

Holding cost

h $4=80$

Lot size Q$4$

$1$ and $2$

$2$ and $3$

$3$ and $4$

$2$ and $4$

Ordering cost

$K3=700$

Holding cost

h$3=60$

Lot size Q$3$