how do you get to 8000 U?

Question 18 Regis Corp. uses two materials, X and Y in making its product. The standards are: Material Standard Mix 3.500 units 1.500 units Standard Unit Price $1.00 per unit $3.00 per unit Standard Cost $3,500 $4,500 Yield 4.000 units Actual production information for April was: Material Actual Mix 30,000 units 20.000 units X Yield 36,000 units What is the materials yield variance? $15,000 F $10,000 U $8,000 U $18.000 u