In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: the average ( arithmetic mean ) monthly income of 4 workers is $ 1000 . after one worker ' s income increases by 50 percent the new average income is $ 1200 . what was the original income of the worker whose monthly income increased ?
Options: a ) $ 1,800 , b ) $ 1,500 , c ) $ 1,300 , d ) $ 1,600 , e ) $ 1,100
d