The PSA benchmark for CPR is 6%. Note: the PSA benchmark increases linearly from 0% to 6% linearly till the 30th month (i.e. increases by 0.2% every month) and thereafter remains steady at 6%. The CPR at 150% of PSA in the 20th month is:

A. 2%

B. 4%

C. 6%

D. 9%