Mathematics Homework Help

I’m working on a probability question and need guidance to help me learn.

(a)A child has a box full of colored building blocks. If he chooses one block without looking, the probability of choosing a green block is 6/17. What are the odds against choosing a green block?

(b) Bill is playing a role-playing game with his friends. He will roll dice to determine if his character casts a spell. The odds in favor of his character casting a spell are 11/8. Find the probability of his character casting a spell.