A =  9 8 7
     6 5 4
     3 2 1

E = 1 0 0
    0 1 0
    0 3 1

A' = 9  8  7
     6  5  4
     21 17 13

E*A = A' => Let's multiply both side with inverse of E:
(E^-1)*E*A = (E^-1)*A' ; (E^-1)*E = I ; I*A = A;
A = (E^-1)*A'

(E^-1) = 1 0 0
         0 1 0
         0 -3 1