How to solve this, really need for this question

Which of the following is most likely the next step in the series? a3z, b6y, c9x, d12w, е15v, f18u

Imogene invested $8,000 in a bank account that pays 8 percent simple interest at the end of each year. her friend invested the same amount in stocks where the growth of the investment is represented as 2,000 times the square root of 2 less than the time lapsed in years. if y1 and y2 represent the amount earned in dollars and t is the time lapsed in years, which system of equations correctly represents the situation?

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?