Can someone help percent problem............

i did every step but i kept getting the wrong answer.....

An instrument store gives a 10% discount to all students off the original cost of an instrument. During a back to school sale an additional 15% is taken off the discounted price. Julie, a student at the local high school, purchases a flute for $306. How much did it originally cost?

P = original price; P1 = price after first discount; P2 = price after second discount

P1 = P - 0.10P and
P2 = P1 - 0.15P1

Julie's cost is P2 = 306 = P1 - 0.15P1 and P1 = 306/(1-0.15) = 360

So, the original cost is 360 = P - 0.10P and P = 360/(1-0.1) = 400 ans.

306 is 85% of the discounted price, p
so
.85 p = 306
and p = 306/.85 = 360

360 is 90% of original price = x
so .90 x = 360
x = 360/.90 = 400