Step-by-step explanation:
AH is negative because the reaction gives out heat (exothermic).
AS is negative because the total entropy of the reactants is greater than that of the products (there are 4 moles of gas on reactant side compared to only 1 mole on the product side). Thus, the reactants are said to be "messier" than the products.
AG is negative at lower temperatures because at low temperatures, -TAS is more negative, resulting in the negative sign of AG.
Hope this helps.