Sample space would be {(3,1),(3,2),(3,3),(3,4),..........(6,6),(1,H),(1,T),(2,H),(2,T).....(5,H),(5,T)}
Events : Coin shows tail {(1,T), (2,T), (4,T), (5,T)}
Atleast one die shows 3 :{(3,1), (3,2), (3,3), (3,4), (3,5), (3,6), (6,3)}
Thus interesection of both is 0
Thus [probability of the event ‘the coin shows a tail / at least one die shows a 3]=0