Question

12 + = 45
?
?
on both sides.

Explanation:

Step1: Isolate $z$ via subtraction

Subtract 12 from both sides.
$12 + z - 12 = 45 - 12$

Step2: Simplify to solve for $z$

Calculate the resulting values.
$z = 45 - 12$

Answer:

$z = 33$
(The operations to fill in the boxes: first box: Subtract 12, second box: Simplify)