Given information:
- The body travels 200 cm in the first two seconds.
- The body travels 220 cm in the next four seconds.

Explanation:
To determine the velocity at the end of the seventh second, we need to understand the concept of velocity and how it is related to distance and time.

Velocity:
Velocity is a vector quantity that expresses the rate at which an object changes its position. It is defined as the displacement of an object per unit of time. Velocity is calculated by dividing the change in position (displacement) by the time it takes for that change to occur.

Displacement:
Displacement refers to the change in position of an object. It is a vector quantity that includes both magnitude (distance) and direction.

Relationship between velocity, distance, and time:
The relationship between velocity, distance, and time can be expressed using the formula:

Velocity = Displacement / Time

Calculating the velocity:
To calculate the velocity at the end of the seventh second, we need to determine the total displacement of the body during the first seven seconds.

Displacement in the first two seconds:
The body travels 200 cm in the first two seconds. This means the displacement during this period is 200 cm.

Displacement in the next four seconds:
The body travels 220 cm in the next four seconds. This implies the displacement during this period is 220 cm.

Total displacement in the first seven seconds:
To determine the total displacement, we add the displacement during the first two seconds to the displacement during the next four seconds.

Total displacement = Displacement in the first two seconds + Displacement in the next four seconds
Total displacement = 200 cm + 220 cm
Total displacement = 420 cm

Calculating the velocity:
Now that we know the total displacement during the first seven seconds is 420 cm, we can calculate the velocity using the formula:

Velocity = Displacement / Time

Velocity = 420 cm / 7 s
Velocity = 60 cm/s

Conclusion:
The velocity at the end of the seventh second from the start is 60 cm/s.