Am i geeking or is there an error in this madas paper

https://preview.redd.it/s4478e2ihplg1.png?width=738&format=png&auto=webp&s=b38bd05bc9c4b65bc741f6def7f41fc4472b663a

Madas FP1 Paper P

When you multiply BA it gives
(1 1)

(0 4)

But this is what my king is saying, it makes it impossible to do part c of the question

https://preview.redd.it/nk54ef6thplg1.png?width=575&format=png&auto=webp&s=2611f5ba7bdc91793ba63cb429bbd28f489f0b7d