ZkSNARKs QAP from Vitalik's blog, how do you calculate R1CS solution vector?

Hi guys. From this blog post:

https://vitalik.ca/general/2016/12/10/qap.html

There's the solution

[1, 3, 35, 9, 27, 30]

Which Vitalik says about calculating it:

You can compute this for yourself by simply "executing" the flattened code above, starting off with the input variable assignment x=3, and putting in the values of all the intermediate variables and the output as you compute them.

But how? Can someone please show me how this is done with the gate vectors/matrices we created? The reason for my confusion is that the constraint equation seems to translate everything to scalars.