Charles Company has prepared a static budget at the beginning of the month. At the end of the month, following information has been retrieved from the records. Static budget: Sales volume: 2,000 units: Price: $55 per unit Variable expense: $13 per unit: Fixed expenses: $35,000 per month Operating Income: $49,000 Actual results: Sales volume: 2,100 units: Price: $60 per unit Variable expense: $15 per unit: Fixed expenses: $40,000 per month Operating Income: $54,500 Calculate the flexible budget variance for operating income