Livemonions Industries uses a kanban system to manage production of the BR$-549$ subassembly. In an eight$-$hour day, they use $900$ units and use containers that can hold $30$ units each. It takes $120$ minutes to fill and move a container of parts to the right place on the BR$-549$ line that is currently rated at a $15\%$ safety factor $.$ How many production hours of inventory are needed?