Given a 4 by 4 matrix, A, as below, find its inverse matrix, A−1.
A=121225341121−1−11−2
The sum of all the elements of A−1 is b. Rounding ∣b∣ to the nearest integer, c. What is the value of mod(c,5), where mod(.) is the modulo operation. (For example, mod(5,2)=1.)