Help plz will mark brainliest to correct answer thx

With this one. will mark brainliest

James is playing his favorite game at the arcade. after playing the game 3 times, he has 8 tokens remaining. he initially had 20 tokens, and the game costs the same number of tokens each time. the number tt of tokens james has is a function of gg, the number of games he plays

What is the sum of the first 8 terms of the geometric series