In an exothermic reaction, there is a transfer of energy to the surroundings in the form of heat energy. The surroundings of the reaction will experience an increase in temperature. Many types of chemical reactions are exothermic, including combustion reactions, respiration & neutralization reactions of bases & acids.
X=r-p. Maybe I don't understand, but I am assuming that you need to isolate for X? you simply subtract p from both sides.<span />
It takes work to push charge through a change of potential.
There's no change of potential along an equipotential path,
so that path doesn't require any work.
To solve this problem it is necessary to apply an energy balance equation in each of the states to assess what their respective relationship is.
By definition the energy balance is simply given by the change between the two states:

Our states are given by



In this way the energy balance for the states would be given by,



Therefore the states of energy would be
Lowest : 0.9eV
Middle :7.5eV
Highest: 8.4eV