If W Varies Directly As 2x - 1, And W = 9 When X = 2, Find X When W = 15?

The direct variation means there is some value k such that
  w = k(2x-1)
We are given
  9 = k(2*2-1) = 3k
  3 = k    (after dividing both sides by 3)
For w = 15, we have
  15 = 3(2x - 1)    (fill in the known values)
  5 = 2x - 1    (divide by 3)
  6 = 2x    (add 1)
  3 = x    (divide by 2)

x is 3 when w is 15.