Define threshold energy and activation energy. How are they related?

Explanation

Threshold energy. It is the minimum amount of energy which the reactant molecules must possess for the effective collisions resulting products.
Activation energy. It is the excess energy required by the reactants to undergo chemical reaction. It is equal to the difference between the threshold energy needed for the reaction and the average kinetic energy of all reacting molecules.
Activation energy = Threshold energy-Average kinetic energy of reactant molecules.
Larger the activation energy slower is the reaction and smaller the activation energy, faster is the reaction.
Consider an exothermic reaction,