Equivalent Units

hi. I am stuck with this question. The answer however is 850 e.u.
Also the workings in the book are shown but they are completely not clear for me to understand. Please help me

Vare produces various inks at its factory. Production details of process1 are as follows:
opening WIP- 400units 60%complete
closing WIP- 600units 20%complete
UNits started-1000 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 complete uses the FIFO method of cost allocation.
What are the equivalent units of production for materials in the period?