maths probability (5m)

please help me probability questions below. please show steps. thank you.
Note that the game will continue until any one of them wins. (please do not use limit to find the answer because I haven't learnt limit yet.)
(a) 2men throw a dice in order and the one first throwing a 6 wins. What aretheir respective probabilities of wining?
(b) 2 men throw 3 dice in order and the one first throwinga sum of 15 wins. What are their respective probabilities of wining?

thank you for your help!