Please help...Is it "of the prevailing" or "on the prevailing"?

Question

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The First Party shall give regular discount by 8% (eight per cent) *of the prevailing* medicine nett price at the time of the transaction to the Second Party for the purchase of ABC products.

Answer 1

of is fine
net has one t.

Answer 2

On.

Would you give a discount of the price or on the price?

Answer 3

Of