Answer:
x=-3
Step-by-step explanation:
x+3=0
-3 -3
x= -3
opposite of addition would be subtraction. since your trying to solve for x You want to get x alone and you subtract by 3 on both sides which would cancel the 3 on the left, leaving:
if you follow the same process on all of them you come to the conclusion that only -3 is a zero in the options listed.
NOTE: When you become more experienced whenever you see expressions like that you'll come to realize that the zero is the opposite sign of the number if it's just x- or x+ a number.
example:
it'll be the opposite sign so since it's a negative the zero of that would be positive 40.
hope this helps!