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.

Paula makes stained-glass windows and sells them to boutique stores. if her costs total $12,000 per year plus $4 per window for the frame. how many windows must she produce to earn a profit of at least $48,000 in one year if she sells the windows for $28 each? 1. define a variable for the situation. 2. write an inequality that represents her profit. note: revenue is money coming in. cost is money going out. profit is the difference between the revenue and the cost. in other words: revenue - costs profit 3.using words, describe how many windows she must sell to have a profit of at least $48,000.