Answer:
The last answer choice, or [-15 14 4a]
[-4 5b -23]
[ ? ? ? ]
Explanation:
In order to subtract matrices, they have to have the same dimensions, which this problem provides(both 3x3) Then, just subtract the numbers on the right from the corresponding numbers on the left. Example: -3-12=-15, which is the top left answer. Repeat with all positions.