You appear to be receiving 3 successive discounts on some
amount (the list price, $lp), to give you your net cost ($nc), and
want to reverse that process. If I have understood correctly,
here is the method:
We know that (((lp - 50%) - 15%) - 7%) = nc
=> lp x 0.5 x 0.85 x 0.93 = nc
=> lp x 0.3953 = nc
=> lp = nc / 0.3953
=> lp = nc x 2.53
Let's check:
List price is $100. Your cost is:
$100 - 50% = $50 - 15% = $42.50 - 7% = $39.53
In reverse, $39.53 x 2.53 = $100.
It works!
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