How is the enlightenment idea of social contract, separation of powers, and natural rights found in the constitution.

Think about it again: natural rights: Locke & hobbes agreed a natural right to life, liberty, and property.
seperation of powers: legislative can make laws the executive can inforce them and the judicial can interpret them those are jobs for each individual branch ONLY.

As far as natural rights go, the unalienable rights of life, liberty, and the pursuit of happiness are broken down into the Bill of Rights, at the start of the constitution. The separation of powers is the creation of the three branches of government, and can be found in the three articles of the constitution. The legislative is found in the first, the executive in the second, and the judicial in the third. You can also find the checks and balances of power here. The idea of the social contract is a simple one, and includes two main components. Mutual defense of rights, and mutual decision by deliberative assembly. One could say that the entire constitution is made up of the social contract, as it was made to defend the people's rights and lives. It is entirely composed of rights and decisions, and concepts of the social contract can be found everywhere within its writing.

Hope that helps!