This was on my lecture page, but I don't understand how they went from step 2 to step 3.

How does 2 & 4 produce -6? and 5 & -3 produce -20?

My homework problem is

A= [3,-5,7]

B= [-1,0,6]

and I'm having trouble trying to figure what to do. I've googled, but I think my terms might be confused.

All I know is that I need to obtain the cross product, and I don't even know what that is