SOLUTION: three seats on a sofa seat can be occupied by a 4 person in how many ways?describe.

We can choose the person to sit in the left-most sofa seat 4 ways.
Having chosen 1 person to sit in the left-most sofa seat, we have 3 
people remaining to choose to sit in the middle sofa seat.
Therefore we can choose the person to sit in the middle sofa 
seat in 3 ways. 
That's 4×3 or 12 ways to choose people to sit in the left and middle
sofa seats.
Having chosen 2 people to sit in the left and middle seats, we have 2
people remaining to choose to sit in the right-most sofa seat.
Therefore we can choose the person to sit in the right-most sofa 
seat 2 ways.

[Note: We can choose the person to remain standing only 1 way]

Answer: 4×3×2 = 24 ways.

Edwin