Given a data set is bell-shaped with a mean of 800 and a standard deviation of 20 what is the interval that should contain at least 95% of the data

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