Answer:
the third one!
Explanation:
Because it says, the SUM of the number, x (or z I can't really see it well) and 1/2, you must add those two together:
1/2 + x
Then it says those two numbers equal to 4, so it would look like this:
1/2 + x = 4
Because you are trying to isolate, and solve for x, you must SUBTRACT 1/2 from both sides of the equal sign:
1/2 + x = 4
-1/2 -1/2
1/2 minus 1/2 would result 0, so there would be x by itself. and 4 minus 1/2 would be 3 and a half ( 3 1/2), so x would be 3 1/2
x = 3 1/2
Hope this helped. If this is incorrect please specify so I can help :)