The correct answer is (A):
He buys x dozen candies at Rs.15 a dozen and x more dozen at Rs.12 a dozen, so the average cost per dozen is Rs. (15 + 12)/2 = Rs.13.5 a dozen.
By selling a dozen at Rs.16.5, he’ll make a profit of Rs.3 per dozen.
To make an overall profit of Rs.150, he needs to sell 50 dozen.