Let H denote the event of a head and T denote the event of a tail.
Total number of elements in sample space =2 x 2 x 2 x 2 = 16 (because in single toss of coin sample space will be 2 and the coin is tossed 4 times)
We define the possible outcomes by an ordered set (w,x, y, z)
w denotes the event the coin is tossed for the first time
x denotes the event the coin is tossed for the second time
y denotes the event the coin is tossed for the third time
z denotes the event the coin is tossed for the fourth time
Sample space
S = {(H,H,H,H),(H,H,H,T),(H,H,T,H),(H,T,H,H),(T,H,H,H),(H,H,T,T),(H,T,H,T),(T,H,H,T),(T,H,T,H),(T,T,H,H),(H,T,T,H),(H,T,T,T),(T,H,T,T),(T,T,H,T),(T,T,T,H),(T,T,T,T)}