Based on Le Chatelier's principle, if a system at equilibrium is disturbed by changes in the temperature, pressure or concentration, then the equilibrium will shift in a direction to undo the effect of the induced change.
The given reaction is endothermic i.e, heat is supplied:
CH4(g) + H2O (g) + heat ↔ 3H2(g) + CO(g)
a) When the temperature is lowered, heat is being removed from the system. The reaction will move in a direction to produce more heat i.e. to the left.
Hence, the pressure of CH4 will increase and equilibrium will shift to the left
b) When the temperature is raised, heat is being added to the system. The reaction will move in a direction to consume the added heat i.e. to the right.
Hence, the pressure of CO will increase and equilibrium will shift to the right
