Matrix multiplication rule: The number of columns of the first matrix must equal the number of rows of the second matrix.
From [A]3×2 and [B]x×y:
Columns of A=2 → Rows of B=x=2.
From [C]3×1:
Rows of A=3 → Rows of C=3.
Columns of B=y=1.
x=2,y=1