Data Sufficiency

how B is sufficient?

First, I'd rewrite the original statement:

-2x > 3y
-x > 3/2 y
x < -3/2 y

Next, I'd rewrite what they give you for #2

2x + 5y - 20 = 0
x + 5/2y - 10 = 0
x = 10 - 5/2y

Now, take this x value and plug it into your rewritten equation from above

10 - 5/2 y < - 3/2y
10 < y

or

y > 10

so you know that y > 10. The question being asked is "is x negative"? You know that x has to be less than -3/2y (from the original statement). You can start picking numbers based on y > 10, (for example y = 11). When y = 11, x has to be less than -3/2 * 11, or less than -33/2. You can do the same for y = 12, 13, etc.

However, the easiest way to solve this is, since you already know that y > 0 is sufficient to solve the problem (from the first statement), then you know that y>10 also has to be sufficient, since y > 10 is included in the set "y > 0". Therefore, B is also sufficient.

(I didn't post the explanation to #1 since it seems like you already got that part)