I am pretty sure the answer is 13
The watch costed $400 before the discount.
76 * 100 = 7,600
7,600 / 19 = 400
The Pythagorean theorem states that the square of the hypotenuse is equal to the sum of the squares of the legs:

The hypotenuse is the side with the greatest length.
Check all options:
1. c=5, a=3, b=4:
true.
2. c=14, a=4, b=11:
false.
3. c=17, a=9, b=14:
false.
4. c=16, a=8, b=14:
false.
5. c=17, a=8, b=15:
true.
Answer: correct options are A and E.
√z = 13 - 8
√z = 5
z = 5²
z = 25
In this case the z can be any number, however z cannot be less than 0 and that is the restriction. (for example; √-1 = irrational number, cannot be solved.)