Hi there!
Please for your future post try to format them a bit nicer (have a look at Please read: make it easier to help you).
That being said, I could identify the issue nonetheless.
does not work because B has size 4x2 and C has size 1x4. You probably wanted to create these with different shapes. I recommend reading the manual section on array literals to figure out how the syntax works:
https://docs.julialang.org/en/v1/manual/arrays/#man-array-literals