[![enter image description here](https://i.stack.imgur.com/7sp5R.png)](https://i.stack.imgur.com/7sp5R.png)

How should i go about solving part (c) of this question? I have computed the reduced row echelon form of the matrix with $U, V$ and $W$ as their columns and i know there is a free variable. However, I'm unsure how to prove that there must be infinitely many solutions.