A ball is droped from a high rise platform `t = 0` starting from rest. After `6 s` another ball is thrown downwards from the same platform with a speed `v`. The two balls meet at `t = 18 s`. What is the value of `v` ?
A. `74 ms^(-1)`
B. `55 ms^(-1)`
C. `40 ms^(-1)`
D. `60 ms^(-1)`