To solve the determinant of a matrix, first, copy the first column and paste it right next to the third column such that there would be 4 columns in total. Then, multiply the numbers diagonally from up to down; add them together. Then subtract from this the sum of the numbers multiplied diagonally from down to up. That would be:
[(1*2*5) + (4*2*1)] - [(1*2*4)+ (5*2*1)] = 0
The answer is C.