Ф = E S is the total flux
Assuming the charge is at the origin-
The flux will be the same for all sides
The total area is 6 m^2
Ф = 6 * 1 N-m^2 / C = 6 N-m^2 / C
The total charge in the box is then 6 C (oulombs)
(Remember F = Newtons = E Q so E is in N/C