Answer:
see below
Explanation:
The number of columns of A is equal to the number of rows of B, so multiplication is possible. It works well to have a calculator do this for you. It involves 27 multiplications and 18 additions, tedious at best.
Each product term is the sum of products ...
p[row=i, column=j] = a[i, 1]b[1, j] +a[i, 2]b[2, j] +a[i, 3]b[3, j]
For example, the product term in the 3rd row, 2nd column is ...
p[3, 2] = a[3, 1]b[1, 2] +a[3, 2]b[2, 2] +a[3, 3]b[3, 2]
= (-4)(-5) +(-1)(3) +(-9)(4) = 20 -3 -36
p[3, 2] = -19