What was the variable rate per unit of output

Question

Taran Company incurred the following costs for the months of January and Feruary. Type of Cost       January         February
Insurance              5,000             5,000
Utilities                  4,000             6,000
Depreciation          3,500             3,500
Materials                10,000           20,000

Assume that output was 5,000 units in January and 10,000 units in Febuary, utility cost is a mixed cost and the fixed cost of utilities was 3,000. What was the variable rate per unit of output for utilities costs in January?