Let the first discount be x%.
Marked Price of shirt = ₹150
Price after first discount =100−x100×Marked Price=100−x100×150
Again 12.5% discount is given on the shirt after initial discount.
Price after second discount = ₹105
⇒ 105=100−12.5100×100−x100×150
105=87.5100×100−x100×150
100−x=105 ×100 ×100150 × 87.5=80
x=100−80=20
So, first discount is 20%.