The Cutting Department's output during the period consists of 18,000 units completed and transferred out, and 4,000 units in ending work in process that were 25% complete as to materials and conversion costs. Beginning inventory was 2,000units that were 25% complete as to materials and conversion costs. Under FIFO method, what are the equivalent units for production for materials?

My teacher has already supplied the answer which is 18500 (this is a study guide). Please somebody explain to me how to do this problem!