Last year, Barnard Company incurred the following costs:

           Direct materials                     $ 50,000
           Direct labor                              20,000
           Manufacturing overhead       130,000
           Selling expense                        40,000
           Administrative expense            36,000

Barnard produced and sold 10,000 units at a price of $31 each.
Prime cost per unit is

  a.  $7.00.
  b.  $20.00.
  c.  $15.00.
  d.  $5.00.
  e.  $27.60.