Math Zero To Hero

Lets try a problem

The amount of tax paid by an executive remains constant despite an increase of tk. 2000 in his salary because the rate of the tax was reduced from 15% to 12%. if 30% of his income was exempted from tax in both the cases what was his salary (in taka) before rise?
A) 8000
B) 10000
C) 12000
D) 13500
E) none of these