If Ψ1 and Ψ2 are two solutions of Schrodinger Wave equation then which of the following is also a solution?

Quantum superposition is a fundamental principle of quantum mechanics that states that linear combinations of solutions to the Schrödinger equation are also solutions of the Schrödinger equation.
The superposition principle states that for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually. 
The principle of linear superposition is a hallmark of quantum theory. It has been confirmed experimentally for photons, electrons, neutrons, and atoms.