What is the determinant of A ?

Distance=slopeslope is -2/4which equals-1/2the distance between these two points is -1/2

9.8? i'm not really sure

Look, when you want to do something like put it like x^2. x2 could mean x² or x₂. so to clear confusion, know the notation. to find the product multiply the x's and you get -8x and the y's and you get 6y. since it's all being multiplied it is just -8x6y, or answer a. although the better answer is -48xy(combining -8 and 6) because you should multiply constants whenever you can.