5z + 15 = 3(z + 1)

To solve the equation \( 5z + 15 = 3(z + 1) \), follow these steps:

1. Distribute the \( 3 \) on the right side of the equation: \[ 5z + 15 = 3z + 3 \]

2. Subtract \( 3z \) from both sides to get all the \( z \) terms on one side: \[ 5z - 3z + 15 = 3 \] This simplifies to: \[ 2z + 15 = 3 \]

3. Next, subtract \( 15 \) from both sides to isolate the \( z \) term: \[ 2z = 3 - 15 \] Which simplifies to: \[ 2z = -12 \]

4. Now, divide both sides by \( 2 \) to solve for \( z \): \[ z = \frac{-12}{2} = -6 \]

Thus, the solution is: \[ z = -6 \]