Answer:
OP = discount amount × 100 / discount %
Explanation:
if I understand this correctly, the actual sale price was 36% (100-64) of the originally marked price.
original price (OP) = 100%
64% of OP = 30
1% of OP = 30/64
OP (100%) = 100 × 30/64
this could be simplified to 100 × 15/32, but this hinders is finding the global formula :
OP = discount amount × 100 / discount %