The given equation is

We have to solve the equation for z.
To solve it for z, we have to move 3 to the right side. 3 is subtracted in the left side, so to get rid of it and move it to right side we have to use reverse operation of subtraction. The reverse operation of subtraction is addition. So to move 3 to the right side we will have to add 3 to both sides.




So we have got the required answer.
The correct option is c here.