What is the constant of proportionality, k, of kevin’s wage? greg’s? savannah?

I’m stuck on this equation, anyone got the answer?

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 t of tokens james has is a function of g, the number of games he plays. write the function’s formula? t=

Answer! if you don’t mind, can you explain