The third λ-calculus problem is a bit more advanced (although still simple):
Reduce the following expression, using the beta-rule, to no more than one term. If the expression cannot be reduced, enter "CAN'T REDUCE".
((λx.(x x)) (λx.(x x)))
((λx.(x x)) (λx.(x x))) cannot be reduced. It is easy to see that applying reduction results with exactly the same expression. So the answer is "CAN'T REDUCE".