If a and b are matrices and ab = i, which of the following represents the value of b? a= [-1, 4 -3, 8]

If the product of 2 matrices are I this means that B is inverse matrix of A.
the matrix A has been given 
if we put symbols for the numbers in matrix A as shown below;

we need to first find the determinant (D)
D = ad - bc
where a = -1 , b = 4, c = -3 and d = 8
substituting these values 
D = -1x8 - (4x-3)
   = -8 +  12 = 4 
to find the inverse we need to exchange a and d and then multiply both b and c by -1

and then have to divide all the terms in matrix by determinant (4)

the simplified inverse matrix B is;