An organisation has the following total costs at two activity levels: Activity level (units) 16,000 22,000 Total costs ($) 135,000 170,000 Variable costs per unit is constant within this range of activity but there is a step up of $5,000 in the total fixed costs when the activity exceeds 17,500 units. What is the total cost at an activity level of 20,000 units? A $163,320 B $158,320 C $160,000 D $154,545