How do you add numbers? i am 1st grader

Francis is getting new carpet tiles in his living room and den. his living room and den are connected. he needs to figure out how much carpet he needs and the cost involved. if each tile costs $2.00 per sq ft, how much would it cost to have new tile put in the den? a) $24 b) $36 c) $48 d) $54 plz awnser soon