SG Co budgeted to make and sell 900 units of product M during September. The standard selling price per unit of M is $27. At the beginning of September, a new competitor entered the market and SG Co was forced to reduce the selling price in order to maintain sales volumes. By the end of September, 900 units had been sold for a total of $18,000. In retrospect it is decided that a realistic standard selling price for September, given the unexpected extra competition, was $18 per unit.
Calculate the sales price planning variance.
$ ______Adverse / Favourable (select the correct option)