To determine John's production for Saturday, we start with his production numbers from Friday:
- Cakes: 12
- Muffins: 50
- Pastries: 42
John's goal for Saturday is to bake 3 times as many of each item. This means we need to multiply each of Friday's production numbers by 3.
1. Cakes on Saturday:
[tex]\[ 12 \times 3 = 36 \][/tex]
2. Muffins on Saturday:
[tex]\[ 50 \times 3 = 150 \][/tex]
3. Pastries on Saturday:
[tex]\[ 42 \times 3 = 126 \][/tex]
Thus, John's production for Saturday can be represented as:
[tex]\[
\left[\begin{array}{c}
36 \\
150 \\
126
\end{array}\right]
\][/tex]
This matches option D in the provided choices.
Therefore, the correct answer is:
[tex]\[
\boxed{\left[\begin{array}{c}36 \\ 150 \\ 126\end{array}\right]}
\][/tex]
