Help!! 10 pts and brainliest!

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

I’m really confused and need to learn this

The table showed price paid per concert ticket on a popular online auction site. what was the average price paid per ticket