The property of equality that justifies the step shown in the equation is the Addition Property of Equality.
This property states that if you add the same value to both sides of an equation, the two sides remain equal. In your example, you added 5 to both sides of the equation:
\( 3z/2 - 5 + 5 = 10 + 5 \)
This simplifies to:
\( 3z/2 = 15 \)
So, the correct response is Addition Property of Equality.