How do i solve this in the quadratic formula?

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

Which equation represents the model shown? a)1/3 divide 1/6 = 2 b)2/3 divide 1/6 = 2/18 c)1/3 divide 1/6 = 1/18 d)2/3 divide 1/6 =4

Acomputer store bought a program at a cost of $10 and sold it for $13. find the percent markup