Cost Accounting

Hi all. Struggling to get my head around the below question from the Kaplan exam kit so if you could help that'd be great. My query regarding question 1: How are they arriving at these figures - "Units started and finished in the period (800 – 400)"? Also, is the 75% just based on the "Three?quarters of the materials..." part of the question? Question 1: Vare produces various inks at its Normanton factory. Production details for Process 1 are as follows: Opening work?in?progress, 1 April 400 units 60% complete Closing work?in?progress, 30 April 600 units 20% complete Units started 1,000 Units finished 800 The degree of completion quoted relates to labour and overhead costs. Three?quarters of the materials are added at the start of the process and the remaining quarter added when the process is 50% complete. The company uses the FIFO method of cost allocation. What are the equivalent units of production for materials in the period? A 1,250 B 1,000 C 850 D 680 Answer 1: Opening inventory completed (400 × 0%) 0 Units started and finished in the period (800 – 400) 400 Closing inventory (600 × 75%) 450 Total equivalent units produced in the period 850 Thanks and hopefully the formatting is okay.