mov     eax, 2          ; y
mul     dword [max_x]   ; eax *= [max_x] <=> (y * max_x) <=> Select line of array
add     eax, 5          ; (y * max_x) + x

mov     [array_2D + eax], dword 23

max_x       dd  5

array_2D:   dd  0, 0, 0, 0, 0
            dd  0, 0, 0, 0, 0
            dd  0, 0, 0, 0, 0
            dd  0, 0, 0, 0, 0