Alhaji Musa Farms Limited incurs the following annual costs: farm manager's salary ₦3,600,000; seeds and fertilisers ₦1,200,000; depreciation of irrigation equipment ₦480,000; casual labour hired per harvest season ₦900,000. Which of these costs is BEST classified as a stepped fixed cost?

A stepped fixed cost remains constant within a relevant range of activity but jumps to a higher level when activity exceeds that range. The farm manager's salary is fixed up to a certain level of output, but an additional manager would be needed if the farm expands significantly beyond its current capacity, making it stepped fixed. Seeds and fertilisers are variable, depreciation is purely fixed, and casual labour is variable.