A state is said to be absorbing if once you're in this state, you don't leave it anymore. x is absorbing if
When you're given the transition matrix, the absorbing states are the ones where there's a 1 in the diagonal.
For question 2), find all the possible paths that go from 1 to 4 (in any given number of steps) and add their probabilities. Maybe doing a sketch will help.
For question 3), which formula are you given ? You must have some lecture notes !