PLEASE HELP ASAP!

On a number line, a number, b. is located the same distance from 0 as another number, a, but in the opposite direction. The number b varies directly with the number a. For example b = 2 when a = -2¾. Which equation represents this direct variation between a and b?
1. b= -a
2. -b= -a
3. b -a=0
4. b(-a)=0​