Finding Sell Price, Givin the Cost

[pierce22884]

I would appreciate any help on how you determine what the sell price should be, knowing that a seller wants to give "X" percent discount and still obtain "X" percent profit:

Question: In order to give his customers a 25 percent discount on the price and still net a 25 percent profit on the cost of an item, at what price should a merchant mark an item if it cost him $16.80?

(A) 21.00

(B) 21.90

(C) 25.20

(D) 26.25

(E) 28.00

The book says that the answer should be (E). If your wondering the source of this question, it comes from the Veritas Quantitative Review Prep book. Thank you in advance for helping.

[palvarez]

x = cost
y = sales price

.75y = 1.25x

3y = 5x

y = 5*16.8/3 = 5*5.6 = 28

[Gmatter2.0]

Expected Profit=25% 16.80=1/4 16.80=4.20
The answer should be greater than 16.80+4.20=21
Eliminate A,B and C

21=75% x
21=3/4 x
x=28

E is the correct Choice...