The total costs incurred at various output levels by Nonsense Company Ltd for a process operation at their Clarendon factory are as follows:

Output Units	Total Costs $
11 500	102 476
12 000	104 730
12 500	106 263
13 000	108 021
13 500	110 727
14 000	113 201

The Variable cost per unit is

a) $0.23

b) $5.50

c) $4.29

d) $6.31