Kaelker Corporation reports that at an activity level of 8,200 units, its total variable cost is $581,380 and its total fixed cost is $85,650. What would be the total cost, both fixed and variable, at an activity level of 8,400 units? Assume that this level of activity is within the relevant range.

a. $683,760

b. $667,030

c. $675,165

d. $681,210