can someone explain why this is the right answer?

Castle Inc. has the following information: Month Amount Cost A January $ 54,000 February $75,600 Units 43,200 86,400 :01 Month Cost B January February Amount $ 28,000 $ 56,000 Units 56,000 112,000 Month Cost C January February Amount $ 27,000 $ 27,000 Units 40,000 80,000 Indicate whether these costs are variable, fixed, or mixed. Answer is complete and correct. Cost A Cost B mixed variable fixed Cost C