At an activity level of 4,500 machine-hours in a month, Novosel Corporation's total variable maintenance and repair cost is $394,830 and its total fixed maintenance and repair cost is $105,570. What would be the total maintenance and repair cost, both fixed and variable, at an activity level of 4,600 units in a month? Assume that this level of activity is within the relevant range. Select one: a. $505,960 b. $511,520 c. $500,400 d. $509,174