For 15:

Make up numbers for x and y and plug them in. Since there are sqroots involved it would be best to choose square numbers. Since x > y, let's say x = 9 and y = 4. The simplified answer would be the 5th root of 16, so you have to find out which of the answer choices also equals the 5th root of 16 by plugging in the same values.

For 11:

When a system of linear equations has no solutions, it means the two lines are parallel (i.e. they have the same slope and different y-intercepts. Expanding option A gives you y = 3x + 9, which has the same slope as the given equation, and a different y intercept. Therefore they are parallel --> A is the right answer