GST DISCOUNT ON MRP

#1
hello everyone
wanted to know about the discount and tax policy applicable on it.
suppose i buy goods worth MRP 1500 with a tag of 30% discount then what is price i have to pay

1) MRP 1550 - 30% = 1085 OR
2) MRP 1550 - 30% = 1085 + TAX

Please help coz stores in mall are charging every individual in same manner