Example $3$EOQ

Checkers purchases $400$ Cell phones at R$1500$ each every month. The phones are sold at R$2000$ each at a steady rate during the year. The ordering costs R$500$ per batch. Insurance, Security and Warehouse costs are $5\%$ of the purchase cost. Calculate the:

$1\mathrm{.}1$ economic order quantity

$1\mathrm{.}2$ the number of orders that should be placed each year