The multistep conversion X → Y occurs through three elementary steps with these potential-energy values relative to the reactants (in kJ·mol⁻¹):
• transition state 1 = 60,
• intermediate 1 = 15,
• transition state 2 = 70,
• intermediate 2 = 30,
• transition state 3 = 45,
• products = −10.
Calculate the activation energy for each of the three forward elementary steps.