Store Deduction

A store advertises that during its Labor Day sale $15 will be deducted from every purchase over $100. In addition, after the deduction is taken, the store offers an early-bird discount of 20% to any person who makes a purchase before 10 a.m. If Hakeem makes a purchase of x dollars, x > 100, at 8 a.m., what, in terms of x, is the cost of Hakeem’s purchase?

(1) 0.20x - 15 (3) 0.85x - 20
(2) 0.20x -3 (4) 0.80x - 12

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Originally Posted by symmetry

A store advertises that during its Labor Day sale $15 will be deducted from every purchase over $100. In addition, after the deduction is taken, the store offers an early-bird discount of 20% to any person who makes a purchase before 10 a.m. If Hakeem makes a purchase of x dollars, x > 100, at 8 a.m., what, in terms of x, is the cost of Hakeem’s purchase?

(1) 0.20x - 15 (3) 0.85x - 20
(2) 0.20x -3 (4) 0.80x - 12

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Correct answer is (4):
Hakkem made purchase of x dollars which is first deducted by $15 which is x-15 and then that price is lower by 20% which means that Hakkem will pay only 80% of (x-15) dollars, so we have equation:
(x-15)*0.80 = 0.80x - 12

Your question is not clear. To find what is the value of x you must know what is the value of Hakeem's purchase.
Let's say he made a total purchase of y dollars.
So we have.
0.80x-12=y
In terms of x solution is:
x=(12+y)/0.80

This question was not clear to me, too.

However, it is in my textbook.

Thanks!