To find the formula for the perimeter of each of Miss Yang's bulletin boards given the length in terms of the width, we can start with the information provided.
The length \( l \) is given by: \[ l = 3w - 6 \]
The perimeter \( P \) of a rectangle can be calculated using the formula: \[ P = 2l + 2w \]
Substituting the expression for the length into the perimeter formula: \[ P = 2(3w - 6) + 2w \]
Now, let's simplify this:
- Distribute the 2 in the first term: \[ P = 6w - 12 + 2w \]
- Combine like terms: \[ P = (6w + 2w) - 12 \] \[ P = 8w - 12 \]
Thus, the simplified expression for the perimeter of each of Miss Yang's bulletin boards is: \[ \boxed{8w - 12} \]