A - the distance between s and 0 is the same as the distance between t and 0. lets find an example: s = -1,3 ; t = 1,3

-1,3......0.....1,3 - suff

-1,3 + 1,3 = 0


B - the best way to see if B is suf is by finding an example : s= -2 ; t=1

-2.......0.......1

zero is between both numbers.

-2 + 1 = -1 ---Insuf

Ok, the easy way is to draw a number line
For example.

2 different number, but with the same distance to 0. s=-1, t=1

I----------I--------I
-1--------0-------1

The distance is 1
Then -1+1=0 A is sufficient

The evaluate B

O is between s and t s=8 t=1

I--------------I--------I
-8------------0-------1
That is true but… -8+1=7 so B is not sufficient.