Ineed finding this sigma-notation sum. i'm not quite sure what to do with the exponent, i have determined a1 = 12, a2=36, a3=108, and a4=324. i notice the pattern of multiplying by 3 each segment, but i'm struggling how to equate this to a form that is simple enough to call an answer.

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