A shirt is marked at a price of Rs. 800. The seller has 100 pieces of this shirt. He sells 60 of them at marked price. Then, he sells some of the remaining shirts at 20% discount, and the remaining at 30% discount. The cost price of a shirt is Rs. 640. In total, he earned a profit of 11.5%. How many shirts did he sell at 30% discount?
1
20
2
24
3
28
4
30
5
16