Given,
MP of the shirt = Rs. 850
Discount = 4 %
Discount allowed = \(\frac{4}{100}\)x 850 = Rs. 34
So,
Selling price of shirt = Rs.(850 – 34) = Rs.816
Profit earned by Jasmine = 20%
CP = \(\frac{100\times S.P.}{100+profit\%}\) = Rs. \(\frac{100\times 816}{100+20}\) = Rs. 680
Cost price of shirt = Rs.680