Si compro 7 cuadernos y 3 lapiceros gasto $ 44 pero si compro 7 lapiceros y 3 cuadernos gasto $ 36 ¿cuánto cuesta 1 lapicero y 1 cuaderno?

The mountain springs water company has two departments, purifying and bottling. the bottling department received 67,000 liters from the purifying department. during the period, the bottling department completed 65,000 liters, including 3,000 liters of work in process at the beginning of the period. the ending work in process was 5,000 liters. how many liters were started and completed during the period?