A. 4
Feedback Step 1: we can assume that Amar joins into business after x months.So Amar money was invested in (12 – x ) months.
Step 2: 76000 x 12 / 57000 x ( 12 – x ) = 2 /1
912000 = 114000 ( 12 – x ) = 114 ( 12 – x ) = 912 = x = 4
After 4 months amar join the business.