Schriever Corporation is an oil well service company that measures its output by the number of wells serviced. The company has provided the following fixed and variable cost estimates that it uses for budgeting purposes. Fixed element Variable Element Revenue Employee salaries and wages Servicing materials Other expenses per month $ 57,200 $ 31,000 per Well Serviced $ 4,500 $ 1,100 $ 600 The planning budget for May was based on 36 wells serviced, but a total of 31 wells were actually serviced in May. The activity variance for revenue for May would have been closest to: