Consider the following reaction:

${\mathrm{N}}_2{\mathrm{O}}_4\rightleftharpoons 2{\mathrm{NO}}_2\left(\mathrm{g}\right);{\mathrm{\Delta H}}^{\mathrm{o}}=58\mathrm{KJ}$

For each of the following cases (a, b), the direction in which the equilibrium shifts is : 

(a)Temperature is decreased
(b)pressure is increased by adding N₂ at constant T.