Where did the 1000 in (4*1000) come from?

Foundational 15 Martinez Company's relevant range of production is 7,500 units to 12,500 units. When it produces and sells 10,000 units, its unit costs are as follows: Amount Per Unit Direct materials . $6.00 Direct labor .......... $3.50 Variable manufacturing overhead ... $1.50 Fixed manufacturing overhead ..... $4.00 Fixed selling expense .... $3.00 Fixed administrative expense ......... $2.00 Sales commissions..................!!!' $1.00 Variable administrative expense......... $0.50 Required: 1. For financial accounting purposes, what is the total amount of product costs incurred to make 10,000 units? Product costs = (DM + DL + VMOH)*Units + F MOH (6+3.50+1.50)*10000 + (4*1000) = $150000