There are 3 numbers on the cube greater than 3 ( 4, 5, & 6)
This means he has a 3/6 = 1/2 chance of doing that.
He has a 1/2 chance of getting tails on the coin.
The probability of doing both would be the probability of the cube roll x the probability of the coin toss:
1/2 x 1/2= 1/4
The answer is 1/4