x + 5=12

7x = 21

b - 2/3 = 5/6

1/5m = 20

45 = 3(x + 1)

22.5 = 1.5x

Mark has $20 in his bank account. He saves $5 each week. How much money does Mark have in his account after 9 weeks? Use w to represent the number of weeks and t to represent the total amount Mark has after any number of weeks.