Hi there.
4(3x + 5y + 2z) + 3(x - z);
12x + 20y + 8z + 3x - 3z;
15x + 20y + 5z.
We can tell that Tom and Chris have the incorrect answers; however, if we go back a step and factor out our current expression, we find ourselves with the following result:
5(3x + 4y + z)
This answer is the exact same that Jenna has; therefore, she has the correct answer.
I hope this helps!