Elena noticed that, nine years ago, her cousin Katie was twice as old as Elena was then. Then Elena said, "In four years, I'll be as old as Katie is now!" If Elena is currently e years old and Katie is k years old, which system of equations matches the story?
a. k - 9 = 2e
e + 4 = k
b. 2k = e - 9
e = k + 4
c. k = 2e - 9
e + 4 = k + 4
d. k - 9 = 2(e - 9)
e + 4 = k
