Here's the question you clicked on:
INT
what is the total probability of finding a particle in a one dimensional box in level n=3 between x = 0 and x = L/6?
Integrate the squared normalized 3rd eigenfunction of the particle in a box Hamiltonian between 0 and L/6. Symmetry and knowing that the 3rd eigenfunction must have 2 nodes will help, but the integral is easy anyway.