What is x less than 10 as a numeric expression and 10 less than x

The table respent two linear functions the equation respented by the first tables is given

Trish receives $450 on the first of each month. josh receives $450 on the last day of each month. both trish and josh will receive payments for next four years. at a discount rate of 9.5 percent, what is the difference in the present value of these two sets of payments?

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