How do you find the variable and selling and admin rate with this info: Selling and admin expenses are known to be a mixed cost; however, there is a lot of uncertainty about the portion that is fixed. Previous year's experience has provided the following info:

The lowest level of sales: 375000 units Total operating expenses: $596,100

Highest level of sales: 750,000 units Total operating expenses: $858,600

It is estimated that selling and admin expenses for the budget year will be about 10% greater than the previous average. These costs are paid in the month in which they occur, with the exception of the only non-cash item: a monthly depreciation of office equipment in the amount of $700. Not included in the above expenses is bad debt expense or warehouse rental.