You find the TP by looking at the diagonal of the matrix:

• TP for Class A: 1
• TP for Class B: 3

You find the FN by adding up each horizontal rows without including the diagonal:

• FN for Class A: 8
• FN for Class B: 3

You find the FP by adding up each vertical column without including the diagonal:

• FP for Class A: 2
• FP for Class B: 2

You find the TN by substracting TP+FN+FP from the total:

• TN for Class A: 18–(1+8+2) = 7
• TN for Class B: 18–(3+3+2) = 10

Hope this helps.