Verified Answer :

You must multiply each element of first row of H and first column of J to get 
a
11 = 47 + -23 + 58 = 28 - 6 + 40 = 62 

You now multiply each element of second row of H and first column of J to get 
a
21 = 6
7 + 13 + -38 = 42 + 3 - 24 = 21