get real price of a discount package applied

First: To get to 521.53 the discount was applied in this way:
X (1 - 0.12) = 521.53
If you solve for X you get this:
X = 521.53 / 0.88 which is approximately 592.65

If you know the final price $dblPrecioFinal and the discount applied $dblPorCiento , the formula, which serves to obtain the real price is:

$dblPrecioReal = $dblPrecioFinal/(1-$dblPorCiento); 

Example:

Demo in Rextester

$dblPrecioFinal=521.53;
$dblPorCiento=.12;

$dblPrecioReal = $dblPrecioFinal/(1-$dblPorCiento); 

echo "PRECIO REAL: ";
echo round($dblPrecioReal,2);

Resultado:

PRECIO REAL: 592.65

How does it work?

• (a) Subtract one from the percentage applied: 1-0.12 = 0.88
• (b) The final price is divided by the value obtained in (a): 521.53/.088
• (c) Result: 592.65 using round to round decimals and use only two decimal digits.