Jasmine allows 4% discount on the marked price of her goods and still earns a profit of 20%

Given,

MP of the shirt $=$ Rs. 850

Discount $=4 \%$

Discount allowed $=$ Rs. $\left(\frac{4}{100} \times 850\right)$

$=$ Rs. 34

Thus, SP of the shirt $=$ Rs. $(850-34)=$ Rs. 816

Now,

Profi $t$ earned by Jasmine $=20 \%$

Thus, CP $=\frac{100 \times \text { SP }}{(100+\text { Profit } \%)}$

$=$ Rs. $\left(\frac{100 \times 816}{100+20}\right)$

$=$ Rs. $\left(\frac{100 \times 816}{120}\right)$

$=$ Rs. 680

Thus, the cost price of the shirt is Rs. 680 .