I need the solution urgently . *** help me

Please clarify your question.

If the list price is P and you apply a 20% discount, the net price is (1-0.2) x P. If you then apply a second discount of 10% on top of that, the new net price is (1-0.1) x (1-0.2) x P. See how it works? Now apply the third discount of 5% and post back what you get.