x denotes the number of times he takes unit step and y denotes the number of times he takes 2 steps, then x+2y=7,
Then we must have x=1,3,5,7
If x=1, the steps will be 1,2,2,2
⇒ number of ways =4!3!=4
If x=3 the steps will be 1,1,1,2,2
⇒ number of ways =5!2!⋅3!=10
If x=5 the steps will be 1,1,1,1,1,2
⇒ number of ways 6C1=6
If x=7 the steps will be 1,1,1,1,1,1,1,1
⇒ number of ways 7C0=1
Hence total number of ways =N=21
⇒N/3=7